Rework makefiles to allow selection of CC/CXX

[pigrew]

This patchset reworks the Makefiles to use the CXX environment variable as the compiler, instead of blindly using g++ (which may not be the proper version, etc...).

It also changes to compiling the generated compiler/parser using C++. The generated code includes C++ header files, and warnings were being generated due to including C++ files from C.

In addition, this code should now compile on the PowerPC platform using clang.

[pigrew]

Apologies about the build errors, "It was working for me". I can't reproduce the build error on my machine, but I'll try to fix it based on the build logs.

[tgrogers]

Did you somehow change the auto-generation of these .c and .h files to .cc/.cpp and .hpp?
What motivated all this makefile change in the first place?

[pigrew]

I've not looked at this in quite a while.

IIRC, some of the C files were including Cpp/hpp headers, and I was getting warnings. At the time, it seemed simpler to just convert everything to C++ instead of trying to tweak the lexer scripts to make everything compile together.

I was also wanting to try to get the whole thing building on the PowerPC RCAC computer that I had been using using an updated version of clang instead of the system-install of gcc.

Also, the "standard" makefile rules use CPPFLAGS for the C preprocessor flags, and CXXFLAGS for C++ flags. The changes to the makefiles change them to use the "standard" environment variables.