cobol: Use *.cc suffix for bison/flex generated C++ files

cobol: Use *.cc suffix for bison/flex generated C++ files

In GCC 12 we've switched to using *.cc suffixes for C++ sources in GCC
sources, including generated files, instead of using *.c suffixes and
compiling them as C++ anyway (that was the case since we've switched
GCC to C++ in GCC 4.8).
I've noticed gcc/cobol has 3 generated files still with c extension
despite clearly having C++ code in it and being compiled as C++.

2025-03-11  Jakub Jelinek  <jakub@redhat.com>

	* Make-lang.in (cobol/parse.c, cobol/cdf.c, cobol/scan.c): Remove.
	(cobol/parse.cc, cobol/cdf.cc, cobol/scan.cc): New goals.
	(cobol/cdf.o): Depend on cobol/cdf.cc rather than cobol/cdf.c.
	(cobol/parse.o): Depend on cobol/parse.cc rather than cobol/parse.c.
	(cobol/scan.o): Depend on cobol/scan.cc rather than cobol/scan.c,
	on cobol/cdf.cc rather than cobol/cdf.c and on cobol/parse.cc rather
	than cobol/parse.c.
	(cobol.srcextra): Depend on cobol/parse.cc cobol/cdf.cc cobol/scan.cc
	rather than cobol/parse.c cobol/cdf.c cobol/scan.c.