Fix crash (in optimized builds) due to invalid metadata operand
- ConstantDataArray is not a valid MDNode operand
- encode function-name strings in metadata by wrapping in an MDString instead

- should resolve reported by http://llvm-jenkins.debian.net/job/llvm-toolchain-quantal-binaries/architecture=amd64,distribution=quantal/173/



git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@183153 91177308-0d34-0410-b5e6-96231b3b80d8