Append -D__func__=__FUNCTION__ to SANITIZER_COMMON_CFLAGS

This way it gets picked up for all sanitizer libs, both sanitizer_common
and asan.  I believe those are the only libs that build with asan.
There should be no need to set the __func__ definition inside
clang_compile.

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@202303 91177308-0d34-0410-b5e6-96231b3b80d8