* Add tests to verify assembler output -- Fix DoNotOptimize.
For things like `DoNotOptimize`, `ClobberMemory`, and even `KeepRunning()`,
it is important exactly what assembly they generate. However, we currently
have no way to test this. Instead it must be manually validated every
time a change occurs -- including a change in compiler version.
This patch attempts to introduce a way to test the assembled output automatically.
It's mirrors how LLVM verifies compiler output, and it uses LLVM FileCheck to run
the tests in a similar way.
The tests function by generating the assembly for a test in CMake, and then
using FileCheck to verify the // CHECK lines in the source file are found
in the generated assembly.
Currently, the tests only run on 64-bit x86 systems under GCC and Clang,
and when FileCheck is found on the system.
Additionally, this patch tries to improve the code gen from DoNotOptimize.
This should probably be a separate change, but I needed something to test.
* Disable assembly tests on Bazel for now
* Link FIXME to github issue
* Fix Tests on OS X
* fix strip_asm.py to work on both Linux and OS X like targets
