bcanalyzer: Use a macro to decode bitcodes, NFC

I'm about to add a whack of missing names for metadata.  Add a macro to
make this easier.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@241015 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed