Print the actual compiler, not its "CMake-id".

Hopefully this will help figure out whether we're using different
compilers for the autotools and CMake builds.

Change-Id: If6d2ee93cd14570c53723140dcedf347600cbe34
Reviewed-on: https://code.wireshark.org/review/3375
Reviewed-by: Guy Harris <guy@alum.mit.edu>