Fixes to allow -fcpp and regression test link changes.

Fixes to allow -fcpp and regression test link changes.

This patch fixes (re-introduces) the -fcpp option and it
migrates more testsuite tcl files to use the new linking mechanism.

2022-06-26  Gaius Mulley  <gaius.mulley@southwales.ac.uk>

gcc/m2/ChangeLog:

	* bnf/gm2l.bnf (ScanArgs): -fcppbegin changed to -fcpp-begin.
	* gm2-compiler/M2DriverOptions.mod (ScanCppArgs):
	-fcppbegin changed to -fcpp-begin, -fcppend changed to
	-fcpp-end.
	* gm2-compiler/M2GenGCC.mod (CodeFinallyEnd): Check
	we are compiling the main module before generating
	the scaffold.
	* gm2-compiler/M2Options.mod (CppRemember): -fcppbegin
	changed to -fcpp-begin.  (CppArg) -fcppbegin
	changed to -fcpp-begin, -fcppend changed to -fcpp-end.
	-fcppprog changed to -fcpp-prog.
	* gm2-compiler/P2SymBuild.mod (BlockEnd): Added assert.
	(PopBlock) bug fix, curModuleSym is popped in
	correct sequence.
	* gm2-lang.cc (gm2_langhook_init_options):
	-fcppbegin changed to -fcpp-begin.  -fcppend changed to
	-fcpp-end.  -fcppprog changed to -fcpp-prog.
	* gm2spec.cc (get_libexec):  New function.
	(gen_gm2_libexec) New function.  (add_exec_dir) New function.
	(lang_register_spec_functions) add exec_prefix.
	* lang-specs.h:	-fcppbegin changed to -fcpp-begin.
	-fcppend changed to -fcpp-end.
	* lang.opt: Uniform internal switch statement used
	where necessary.  -fcppbegin changed to -fcpp-begin.
	-fcppend changed to -fcpp-end.  -fcppprog= changed to -fcpp-prog=.

libgm2/Changelog:

	* libm2iso/m2rts.h: (New file).

Signed-off-by: Gaius Mulley <gaius.mulley@southwales.ac.uk>