COFF: Friendlier undefined symbol errors.

COFF: Friendlier undefined symbol errors.

Summary:
This change does three things:
- Try to find the file and line number of an undefined symbol
  reference by reading codeview debug info.
- Try to find the name of the function or global variable with the
  undefined symbol reference by searching the object file's symbol
  table.
- Prints the information in the same style as the ELF linker.

Differential Revision: https://reviews.llvm.org/D45467

llvm-svn: 330235