Support C++-specific selftests

Support C++-specific selftests

gcc/ChangeLog:
	* Makefile.in (SELFTEST_FLAGS): Drop "-x c", moving it to...
	(C_SELFTEST_FLAGS): New.
	(CPP_SELFTEST_FLAGS): New.
	(SELFTEST_DEPS): New, from deps of s-selftest.
	(C_SELFTEST_DEPS): New, from deps of s-selftest.
	(CPP_SELFTEST_DEPS): New.
	(selftest): Add dependency on s-selftest-c++.
	(s-selftest): Rename to...
	(s-selftest-c): ...this, moving deps to SELFTEST_DEPS
	and C_SELFTEST_DEPS, and using C_SELFTEST_FLAGS rather
	than SELFTEST_FLAGS.
	(selftest-gdb): Rename to...
	(selftest-c-gdb): ...this, using C_SELFTEST_DEPS and
	C_SELFTEST_FLAGS.
	(selftest-gdb): Reintroduce as an alias for selftest-c-gdb.
	(selftest-valgrind): Rename to...
	(selftest-c-valgrind): ...this, using C_SELFTEST_DEPS and
	C_SELFTEST_FLAGS.
	(selftest-valgrind): Reintroduce as an alias for
	selftest-c-valgrind.
	(s-selftest-c++): New.
	(selftest-c++-gdb): New.
	(selftest-c++-valgrind): New.

gcc/c-family/ChangeLog:
	* c-common.c (selftest::c_family_tests): New.
	* c-common.h (selftest::run_c_tests): Move decl to c/c-lang.h.
	(selftest::c_family_tests): New decl.

gcc/c/ChangeLog:
	* c-lang.c (selftest::run_c_tests): Move body to c_family_tests,
	and call that instead.
	* c-tree.h (selftest::run_c_tests): New decl.

gcc/cp/ChangeLog:
	* cp-lang.c (LANG_HOOKS_RUN_LANG_SELFTESTS): Define as
	selftest::run_cp_tests.
	(selftest::run_cp_tests): New function.
	* cp-tree.h (selftest::run_cp_tests): New decl.

From-SVN: r250030