llvm-cxxfilt: fix program description

Fix a silly copy-paste error in the tool description.  Take the
opportunity to add crash stack printing which will hopefully never be
needed.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@292579 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed