PR19562: DebugInfo temporary MDNode leak: Don't include a temporary node to...

PR19562: DebugInfo temporary MDNode leak: Don't include a temporary node to replace with a variable list for methods, since they're always declarations and thus never include variables

This field is used for a list of variables to ensure they are not lost
during optimization (they're only included when optimizations are
enabled).

llvm-svn: 208159