Dump additional debugging information.

For autotools, dump CC, CFLAGS, CXX, and CXXFLAGS.

For CMake, dump CMAKE_C_COMPILER_ID and CMAKE_CXX_COMPILER_ID.

Hopefully this will help figure out why CMake builds catch different
warnings from autotools builds.

Change-Id: I26955ad955f60e8bad248562fa87963a3a1bb42f
Reviewed-on: https://code.wireshark.org/review/3365
Reviewed-by: Guy Harris <guy@alum.mit.edu>