c++/modules: Clean up include translation [PR110980]

c++/modules: Clean up include translation [PR110980]

Currently the handling of include translation is confusing to read,
using a tri-state integer without much clarity on what different states
mean.  This patch cleans this up to use explicit enumerators indicating
the different possible states instead, and fixes a bug where the option
'-flang-info-include-translate' ended being accidentally unusable.

	PR c++/110980

gcc/cp/ChangeLog:

	* module.cc (maybe_translate_include): Clean up.

gcc/testsuite/ChangeLog:

	* g++.dg/modules/inc-xlate-2_a.H: New test.
	* g++.dg/modules/inc-xlate-2_b.H: New test.
	* g++.dg/modules/inc-xlate-3.h: New test.
	* g++.dg/modules/inc-xlate-3_a.H: New test.

Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>