[msan] Stop demangling function name in the stack origin report.

This was done by calling __cxa_demangle directly, which is bad
when c++abi library is instrumented. The following line always
contains the demangled name (when running with a symbolizer) anyway.


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@212929 91177308-0d34-0410-b5e6-96231b3b80d8