llvm-undname: Add a -raw-file flag to pass a raw buffer to microsoftDemangle

The default handling splits input into lines. Since
llvm-microsoft-demangle-fuzzer doesn't do this, oss-fuzz produces inputs
that only trigger crashes if the input isn't split into lines. This adds
a hidden flag -raw-file which passes file contents to microsoftDemangle() in
the same way the fuzzer does, for reproducing oss-fuzz reports.

Also change llvm-undname to have a non-0 exit code for invalid symbols.

Differential Revision: https://reviews.llvm.org/D60771

llvm-svn: 358485