[GRASS5] C++ compilation

[Paul Kelly]

I fixed a bug (committed to CVS) in src/CMD/generic/gmake.sh where the new
support for .cc files caused a problem in modules that use lex/yacc: where
the .c file was not existing at the start of compilation and a .cc extension
was appended instead of .c (y.tab.c, lex.yy.c).

I don't think it looks right yet however as $(CC) is used to compile the
C++ files; probably it should be $(CPP) or something and configure should
check for a C++ compiler on the system?

Paul