PR modula2/109336 - The -fmod= and -fdef= options do not work

PR modula2/109336 - The -fmod= and -fdef= options do not work

The -fmod= and -fdef= options do not work.  After the linking
re-implementation and subsequent restructuring the -fmod= amd -fdef= are
now broken.  This patch adds -fmod= and -fdef= processing into gm2spec.cc.
It also reduces the complexity of extension handling within M2Search
by storing the preceeding "." in the extension.

gcc/m2/ChangeLog:

	PR modula2/109336
	PR modula2/109315
	* gm2-compiler/M2FileName.mod (CalculateFileName): Simplified by
	ensuring the extension contains the ".".
	(CalculateStemName): Re-formatted.
	(ExtractExtension): Re-formatted.
	(ExtractModule): Re-formatted.
	* gm2-compiler/M2Options.def (setdefextension): Add block comment.
	(setmodextension): Add block comment.  Re-formatted.
	* gm2-compiler/M2Options.mod (setdefextension): Add block comment.
	(setmodextension): Add block comment.  Re-formatted.
	* gm2-compiler/M2Search.mod (FindSourceDefFile): Use
	DefaultDefExt.
	(DefaultDefExt): New constant.
	(DefaultModExt): New constant.
	(FindSourceModFile): Use DefaultModExt.
	* gm2-gcc/m2decl.cc (m2decl_DeclareKnownVariable): Correct
	spelling.
	* gm2spec.cc (M2SOURCE): New constant.
	(LANGSPEC): New value.
	(MATHLIB): New value.
	(WITHLIBC): New value.
	(SKIPOPT): New value.
	(lang_specific_driver): Replace seen_module_extension bool with
	module_extension char *.  Detect -fmod= and remember extension.
	Use the extension to detect modula-2 source and mark it as such.

gcc/testsuite/ChangeLog:

	PR modula2/109336
	* gm2/link/nondefaultext/pass/hello.md: New test.
	* gm2/link/nondefaultext/pass/liba.dm: New test.
	* gm2/link/nondefaultext/pass/liba.md: New test.
	* gm2/link/nondefaultext/pass/link-nondefaultext-pass.exp: New test.

Signed-off-by: Gaius Mulley <gaiusmod2@gmail.com>