[sanitizer_common] Check 'demangle' flag in StripFunctionName and DemangleFunctionName

To allow getting the original stack trace.

Reviewed By: dvyukov

Differential Revision: https://reviews.llvm.org/D151411

GitOrigin-RevId: 215a742b8804f33c84f866d3c5aacd8d35129c49
1 file changed