[asan] make asan work with 7fff8000 offset and prelink

When prelink is installed in the system, prelink-ed
libraries map between 0x003000000000 and 0x004000000000 thus occupying the shadow Gap,
so we need so split the address space even further, like this:
|| [0x10007fff8000, 0x7fffffffffff] || HighMem    ||
|| [0x02008fff7000, 0x10007fff7fff] || HighShadow ||
|| [0x004000000000, 0x02008fff6fff] || ShadowGap3 ||
|| [0x003000000000, 0x003fffffffff] || MidMem     ||
|| [0x00087fff8000, 0x002fffffffff] || ShadowGap2 ||
|| [0x00067fff8000, 0x00087fff7fff] || MidShadow  ||
|| [0x00008fff7000, 0x00067fff7fff] || ShadowGap  ||
|| [0x00007fff8000, 0x00008fff6fff] || LowShadow  ||
|| [0x000000000000, 0x00007fff7fff] || LowMem     ||

Do it only if necessary.

Also added a bit of profiling code to make sure that the
mapping code is efficient.

Added a lit test to simulate prelink-ed libraries.
Unfortunately, this test does not work with binutils-gold linker.
If gold is the default linker the test silently passes.

Also replaced
__has_feature(address_sanitizer)
with
__has_feature(address_sanitizer) || defined(__SANITIZE_ADDRESS__)
in two places.

Patch partially by Jakub Jelinek.



git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@175263 91177308-0d34-0410-b5e6-96231b3b80d8
[ASan] Fix https://code.google.com/p/address-sanitizer/issues/detail?id=159
MaybeReexec() does now a tricky job to manage DYLD_INSERT_LIBRARIES in a safe way.

Because we're using library interposition, it's critical for an instrumented app
to be executed with the runtime library present in DYLD_INSERT_LIBRARIES list.
Therefore if it's initially missing in that list, we append the runtime library name
to the value of DYLD_INSERT_LIBRARIES and then exec() ourselves.

On the other hand, some of the apps exec()ed by our program may not want to have
ASan runtime library preloaded, so we remove the runtime library from the
DYLD_INSERT_LIBRARIES if it's already there.

Users may want to preload other libraries using DYLD_INSERT_LIBRARIES, so we preserve those.



git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@175276 91177308-0d34-0410-b5e6-96231b3b80d8
[ASan] make variable unsigned to silence the warning

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@175284 91177308-0d34-0410-b5e6-96231b3b80d8
[ASan] make variables unsigned to silence warnings - attempt 2

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@175285 91177308-0d34-0410-b5e6-96231b3b80d8