modula-2, driver, Front end: Revise handling of I and L paths [PR108182].

modula-2, driver, Front end: Revise handling of I and L paths [PR108182].

The adds the includes in the FE as done in other GCC languages.
It also revises the library handling to avoid additional -L options
from hiding LIBDIR.

For the include/import paths as presented to the front end initialisation,
we capture them and then arrange to emit the 'standard library' paths in
the same order as specified for C.

The specs are tidied up.

The use of the internal prefix also fixes searching in a relocated compiler.

Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
	PR modula2/108182
	PR modula2/108480

gcc/m2/ChangeLog:

	* Make-lang.in: Pass libsubdir to the language init
	build.
	* gm2-lang.cc (INCLUDE_VECTOR): Define.
	(add_one_import_path): New.
	(add_m2_import_paths): New.
	(gm2_langhook_post_options): Arrange to add the include
	paths (and add the system ones) in the same order as C
	uses.
	* gm2spec.cc (build_archive_path): Remove.
	(add_default_combination): Remove.
	(add_default_archives): Remove.
	(add_default_libs): We no longer need a '-L' option, just
	emit the -l and each library in use.
	(build_include_path): Remove.
	(add_include): Remove.
	(add_default_includes): Remove.
	(library_installed): Remove.
	(check_valid_library): Remove.
	(check_valid_list): Remove.
	(convert_abbreviation): Diagnose unhandled cases.
	(lang_specific_driver): Skip options where we will add back
	a validated version.
	* lang-specs.h (M2CPP): Reformat, append %I when -fcpp is not
	in use.  Revise the cc1gm2 spec to omit mentioning options that
	are handled in the c pre-processor line.
	* lang.opt: Allow preprocessing and path options as input to the
	cc1gm2 invocation, so that they can be passed to the preprocessor
	invocation.