Disable the -gmlt optimization implemented in r218129 under Darwin due to issues with dsymutil.

r218129 omits DW_TAG_subprograms which have no inlined subroutines when
emitting -gmlt data. This makes -gmlt very low cost for -O0 builds.

Darwin's dsymutil reasonably considers a CU empty if it has no
subprograms (which occurs with the above optimization in -O0 programs
without any force_inline function calls) and drops the line table, CU,
and everything in this situation, making backtraces impossible.

Until dsymutil is modified to account for this, disable this
optimization on Darwin to preserve the desired functionality.
(see r218545, which should be reverted after this patch, for other
discussion/details)

Footnote:
In the long term, it doesn't look like this scheme (of simplified debug
info to describe inlining to enable backtracing) is tenable, it is far
too size inefficient for optimized code (the DW_TAG_inlined_subprograms,
even once compressed, are nearly twice as large as the line table
itself (also compressed)) and we'll be considering things like Cary's
two level line table proposal to encode all this information directly in
the line table.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218702 91177308-0d34-0410-b5e6-96231b3b80d8
[x86] Rework all of the 128-bit vector shuffle tests with my handy test
updating script so that they are more thorough and consistent.

Specific fixes here include:
- Actually test VEX-encoded AVX mnemonics.
- Actually use an SSE 4.1 run to test SSE 4.1 features!
- Correctly check instructions sequences from the start of the function.
- Elide the shuffle operands and comment designator in a consistent way.
- Test all of the architectures instead of just the ones I was motivated
  to manually author.

I've gone back through and fixed up any egregious issues I spotted. Let
me know if I missed something you really dislike.

One downside to this is that we're now not as diligently using FileCheck
variables for registers. I would be much more concerned with this if we
had larger register usage, but there just aren't that interesting of
register choices here and most of the registers are constrained by the
ABI. Ultimately, I don't think this is likely to be the maintenance
burden for these tests and updating them again should be staright
forward.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218707 91177308-0d34-0410-b5e6-96231b3b80d8
Adjust test case addition in r218702 so as not to fail when the X86 target isn't built.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218708 91177308-0d34-0410-b5e6-96231b3b80d8
[x86] Update the exact FileCheck syntax of the 256-bit and 512-bit
shuffle tests to match that used in the script I posted and now used
consistently in 128-bit tests.

Nothing interesting changing here, just using the label name as the
FileCheck label and a slightly more general comment marker consumption
strategy.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218709 91177308-0d34-0410-b5e6-96231b3b80d8
[x86] Add AVX1 and AVX2 testing to all of the 128-bit shuffle test
cases.

While clearly we don't need the AVX vector width, these ISA extensions
often cause us to select different instructions and we should cover them
even with the narrow vector width.

Also, while here, nuke the stress_test2 contents. There is no reason to
try to FileCheck this entire body when it is mostly a test for
successfully surviving the code generator.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218710 91177308-0d34-0410-b5e6-96231b3b80d8