[compiler-rt] [CMake] Build compiler-rt with no optimizations if the flag says so

[george.karpenkov]

Summary

Without this change, compiler-rt gets compiled with optimizations when inside release build, even if the flag for compiling in debug mode for compiler-rt was specifically set.

[kcc]

LGTM
Just curious, what's the use case?

Also, please triple-check that the default build still uses -O3

[george.karpenkov]

@kcc it's often useful to have a compiler compiled with optimizations if your tests involve compiling stuff.
Otherwise running those tests takes forever.
Yet still, even in that configuration one might wish to attach a debugger to see what symbolication/coverage instrumentation/etc is doing.

CMakeLists.txt

 endif()
 
 append_list_if(COMPILER_RT_DEBUG -DSANITIZER_DEBUG=1 SANITIZER_COMMON_CFLAGS)
 
 # Build with optimization, unless we're in debug mode. If we're using MSVC,
 # always respect the optimization flags set by CMAKE_BUILD_TYPE instead.
 if(NOT COMPILER_RT_DEBUG AND NOT MSVC)
   list(APPEND SANITIZER_COMMON_CFLAGS -O3)
+else()
+  list(APPEND SANITIZER_COMMON_CFLAGS -O0)
 endif()
 
 # Determine if we should restrict stack frame sizes.
 # Stack frames on PowerPC and Mips and in debug biuld can be much larger than
 # anticipated.
 # FIXME: Fix all sanitizers and add -Wframe-larger-than to
 # SANITIZER_COMMON_FLAGS
 if(COMPILER_RT_HAS_WFRAME_LARGER_THAN_FLAG AND NOT COMPILER_RT_DEBUG