[Sanitizer tests] Fix a comment that got out of sync with the #if

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@208602 91177308-0d34-0410-b5e6-96231b3b80d8
Move .subsections_via_symbols directives into DEFINE_COMPILERRT_PRIVATE_FUNCTION

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@208603 91177308-0d34-0410-b5e6-96231b3b80d8