1. remove all window interface bits from compiler.370, and have
the preceding include files set some variables to control
the behavior of compiler.370 when it comes to c++.
2. some more common Makefile lines into sys/unix/hints/include/multiw-3.370.
3. make it so you can pass cppregex=1 on the Make command line to build with
sys/share/cppregex.cpp instead of posixregex.c
4. fix sys/share/cppregex.cpp so that it will build with clang compiler
(required an additional header include). I don't know if it would have
worked with g++ without that change. The include can be placed into an #ifdef
block if there's an issue with the change on other compilers.
5. Anything that needs to compile using c++ (Qt, sys/share/cppregex.cpp) can
just ensure that CPLUSPLUS_NEEDED Makefile variable is set above the lines
in compiler.370 to ensure that things get set up for c++. It no longer
checks specifically for Qt. That is what sys/unix/hints/include/multiw-2.370
does now.