[compiler-rt] [compiler-rt][test] Apply CFLAGS from sanitizer_common to all tests (PR #120798)

[Aaron Puchert via llvm-commits]

aaronpuchert wrote:

In general, I don't know what the desired semantics of `CMAKE_SYSROOT` is. It's currently handled inconsistently, and it seems that Google's builds rely on that inconsistency.
1. It should probably apply to the build of LLVM (+ components) itself.
2. Should it apply to building the tests?
3. Should it apply to running the tests?

The answer to the second question was "sometimes" and I've tried to change it to "always" here. This should fix the issue after #119071, where the sysroot was older, but here it seems like the sysroot is newer? And then we would also need to run the tests against the sysroot? But maybe this is going to break another build, where the sysroot isn't actual meant for running stuff against it?

https://github.com/llvm/llvm-project/pull/120798