We were previously already detecting when a variable name was redefined
as a function, but not the inverse. The fix involves inserting the
unmangled function name into the symbol table.

Change-Id: I0efd1309d45f004c8d1c5ceb864e08c2ebe22f1d
Reviewed-on: https://swiftshader-review.googlesource.com/16048Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>