mame: disable LTO on OS X 10.7 and below

Recent addition of LTO (link time optimization) in the formula seems to be broken on older OS X. It builds without problem, but crashes on startup at least with my 10.7 (Lion). An exactly same issue found with 0.155 formula as well.

It's probably due to an obsolete version of clang which is no longer updated/supported as Xcode and OS itself are. As an workaround, the formula is updated to ensure that LTO is only enabled on 10.8 (Mountain Lion) and above.

FYI, here is a part of crash log from mame 0.156 with SDL2:

```
Crashed Thread:  0  Dispatch queue: com.apple.main-thread

Exception Type:  EXC_BAD_ACCESS (SIGSEGV)
Exception Codes: 0x000000000000000d, 0x0000000000000000

VM Regions Near 0:
-->
    __TEXT                 00000001072ef000-000000010ac53000 [ 57.4M] r-x/rwx SM=COW  /usr/local/Cellar/mame/0.156/bin/mame

Application Specific Information:
objc[5802]: garbage collection is OFF

Thread 0 Crashed:: Dispatch queue: com.apple.main-thread
0   libunwind.dylib                    0x00007fff8fd86fe6 libunwind::CompactUnwinder_x86_64<libunwind::LocalAddressSpace>::stepWithCompactEncodingFrameless(unsigned int, unsigned long long, libunwind::LocalAddressSpace&, libunwind::Registers_x86_64&, bool) + 630
1   libunwind.dylib                    0x00007fff8fd8520c libunwind::CompactUnwinder_x86_64<libunwind::LocalAddressSpace>::stepWithCompactEncoding(unsigned int, unsigned long long, libunwind::LocalAddressSpace&, libunwind::Registers_x86_64&) + 52
2   libunwind.dylib                    0x00007fff8fd85171 libunwind::UnwindCursor<libunwind::LocalAddressSpace, libunwind::Registers_x86_64>::step() + 69
3   libobjc.A.dylib                    0x00007fff8e9b9294 objc_addExceptionHandler + 82
4   com.apple.CoreFoundation           0x00007fff91f1ca34 _CFDoExceptionOperation + 308
5   com.apple.AppKit                   0x00007fff8ad21696 _NSAppKitLock + 73
6   com.apple.AppKit                   0x00007fff8af1c0c3 +[NSScroller initialize] + 95
7   libobjc.A.dylib                    0x00007fff8e9b4662 _class_initialize + 320
8   libobjc.A.dylib                    0x00007fff8e9b4517 prepareForMethodLookup + 237
9   libobjc.A.dylib                    0x00007fff8e9b42bb lookUpMethod + 63
10  libobjc.A.dylib                    0x00007fff8e9b1f3c objc_msgSend + 188
11  com.apple.AppKit                   0x00007fff8ad803c6 -[NSWindow _surfaceOrderedInWindow:] + 44
12  com.apple.AppKit                   0x00007fff8b1fdb2e -[NSOpenGLContext setView:] + 885
13  libSDL2-2.0.0.dylib                0x000000010d3a3db8 -[SDLOpenGLContext setWindow:] + 217
14  libSDL2-2.0.0.dylib                0x000000010d3a453f Cocoa_GL_MakeCurrent + 84
15  libSDL2-2.0.0.dylib                0x000000010d3a4264 Cocoa_GL_CreateContext + 916
16  libSDL2-2.0.0.dylib                0x000000010d3a01ac SDL_GL_CreateContext_REAL + 84
17  mame                               0x00000001094fc455 _ZL21drawogl_window_createP15sdl_window_infoii + 303
18  mame                               0x000000010940dff8 _ZL18complete_create_wtPvi + 496
19  mame                               0x000000010940be64 sdl_osd_interface::video_init() + 4350
20  mame                               0x00000001092cc35a osd_interface::init_subsystems() + 18
21  mame                               0x0000000108965446 sdl_osd_interface::init(running_machine&) + 1928
22  mame                               0x00000001091f1722 running_machine::run(bool) + 1676
23  mame                               0x0000000109061c6c machine_manager::execute() + 4688
24  mame                               0x0000000107350038 main + 3511
25  mame                               0x00000001072f39f4 start + 52
```

And here is a log from mame 0.155 with SDL 1.2:

```
Crashed Thread:  0  Dispatch queue: com.apple.main-thread

Exception Type:  EXC_BAD_ACCESS (SIGSEGV)
Exception Codes: 0x000000000000000d, 0x0000000000000000

VM Regions Near 0:
-->
    __TEXT                 000000010ca23000-000000011032e000 [ 57.0M] r-x/rwx SM=COW  /usr/local/Cellar/mame/0.155/bin/mame

Application Specific Information:
objc[41468]: garbage collection is OFF

Thread 0 Crashed:: Dispatch queue: com.apple.main-thread
0   libunwind.dylib                    0x00007fff940affe6 libunwind::CompactUnwinder_x86_64<libunwind::LocalAddressSpace>::stepWithCompactEncodingFrameless(unsigned int, unsigned long long, libunwind::LocalAddressSpace&, libunwind::Registers_x86_64&, bool) + 630
1   libunwind.dylib                    0x00007fff940ae20c libunwind::CompactUnwinder_x86_64<libunwind::LocalAddressSpace>::stepWithCompactEncoding(unsigned int, unsigned long long, libunwind::LocalAddressSpace&, libunwind::Registers_x86_64&) + 52
2   libunwind.dylib                    0x00007fff940ae171 libunwind::UnwindCursor<libunwind::LocalAddressSpace, libunwind::Registers_x86_64>::step() + 69
3   libobjc.A.dylib                    0x00007fff92ce2294 objc_addExceptionHandler + 82
4   com.apple.CoreFoundation           0x00007fff96245a34 _CFDoExceptionOperation + 308
5   com.apple.AppKit                   0x00007fff8f04a696 _NSAppKitLock + 73
6   com.apple.AppKit                   0x00007fff8f04a5d4 _NSCursorLock + 62
7   com.apple.AppKit                   0x00007fff8f1fa58a +[NSCursor pointingHandCursor] + 15
8   com.apple.AppKit                   0x00007fff8f1fa127 -[NSTextViewSharedData _commonInit] + 774
9   com.apple.AppKit                   0x00007fff8f1f9e17 -[NSTextViewSharedData init] + 65
10  com.apple.AppKit                   0x00007fff8f1f9d9d _getAndCacheSharedData + 108
11  com.apple.AppKit                   0x00007fff8f1f9d1b -[NSTextView(NSSharing) typingAttributes] + 42
12  com.apple.AppKit                   0x00007fff8f1f9c08 -[NSTextView(NSPrivate) _addToTypingAttributes:value:] + 43
13  com.apple.AppKit                   0x00007fff8f1f9bd0 -[NSTextView(NSPrivate) _commonInitState] + 253
14  com.apple.AppKit                   0x00007fff8f1f9938 -[NSTextView initWithFrame:textContainer:] + 159
15  com.apple.AppKit                   0x00007fff8f1f83b1 -[NSTextView initWithFrame:] + 477
16  libSDL-1.2.0.dylib                 0x00000001129eecb8 QZ_VideoInit + 396
17  libSDL-1.2.0.dylib                 0x00000001129e6091 SDL_VideoInit + 509
18  libSDL-1.2.0.dylib                 0x00000001129c93ed SDL_InitSubSystem + 113
19  libSDL-1.2.0.dylib                 0x00000001129c94a1 SDL_Init + 23
20  mame                               0x000000010e45d87c sdl_osd_interface::init(running_machine&) + 654
21  mame                               0x000000010e8e5b84 running_machine::run(bool) + 1676
22  mame                               0x000000010e75e400 machine_manager::execute() + 4688
23  mame                               0x000000010e07a1b6 -[SDLMain applicationDidFinishLaunching:] + 3552
24  com.apple.Foundation               0x00007fff94f1cd0e __-[NSNotificationCenter addObserver:selector:name:object:]_block_invoke_1 + 47
25  com.apple.CoreFoundation           0x00007fff961fe7ba _CFXNotificationPost + 2634
26  com.apple.Foundation               0x00007fff94f08fc3 -[NSNotificationCenter postNotificationName:object:userInfo:] + 65
27  com.apple.AppKit                   0x00007fff8f053e2b -[NSApplication _postDidFinishNotification] + 212
28  com.apple.AppKit                   0x00007fff8f053b91 -[NSApplication _sendFinishLaunchingNotification] + 78
29  com.apple.AppKit                   0x00007fff8f052858 -[NSApplication(NSAppleEventHandling) _handleAEOpenEvent:] + 242
30  com.apple.AppKit                   0x00007fff8f0525b9 -[NSApplication(NSAppleEventHandling) _handleCoreEvent:withReplyEvent:] + 330
31  com.apple.CoreFoundation           0x00007fff96248541 -[NSObject performSelector:withObject:withObject:] + 65
32  com.apple.Foundation               0x00007fff94f3f7c7 __-[NSAppleEventManager setEventHandler:andSelector:forEventClass:andEventID:]_block_invoke_1 + 101
33  com.apple.Foundation               0x00007fff94f3e74e -[NSAppleEventManager dispatchRawAppleEvent:withRawReply:handlerRefCon:] + 283
34  com.apple.Foundation               0x00007fff94f3e5dc _NSAppleEventManagerGenericHandler + 105
35  com.apple.AE                       0x00007fff918c1c25 aeDispatchAppleEvent(AEDesc const*, AEDesc*, unsigned int, unsigned char*) + 200
36  com.apple.AE                       0x00007fff918c1b03 _ZL25dispatchEventAndSendReplyPK6AEDescPS_ + 38
37  com.apple.AE                       0x00007fff918c19f7 aeProcessAppleEvent + 250
38  com.apple.HIToolbox                0x00007fff94387b69 AEProcessAppleEvent + 102
39  com.apple.AppKit                   0x00007fff8f04f9c5 _DPSNextEvent + 1247
40  com.apple.AppKit                   0x00007fff8f04f07d -[NSApplication nextEventMatchingMask:untilDate:inMode:dequeue:] + 135
41  com.apple.AppKit                   0x00007fff8f04b9b9 -[NSApplication run] + 470
42  mame                               0x000000010ca82629 main + 1280
43  mame                               0x000000010ca27a54 start + 52
```