llvm-pdbdump: Improve printing of functions and signatures.

llvm-pdbdump: Improve printing of functions and signatures.

This correctly prints the function pointers, and also prints
function signatures for symbols as opposed to just types.  So
actual functions in your program will now be printed with full
name and signature, as opposed to just name as before.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@229129 91177308-0d34-0410-b5e6-96231b3b80d8