llvm-cov: Added checks for ident, checksum, name.

Added additional checks for the Identifier, CfgChecksum and Name for
each GCOVFunction. Also added function names in error messages.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@196356 91177308-0d34-0410-b5e6-96231b3b80d8