Move docs for -Wuse-after-free and -Wuseless-cast [PR111693]

These options were categorized as C++ options, but they apply to all
C-family languages.

gcc/ChangeLog
	PR c/111693
	* doc/invoke.texi (Option Summary): Move -Wuseless-cast
	from C++ Language Options to Warning Options.  Add entry for
	-Wuse-after-free.
	(C++ Dialect Options): Move -Wuse-after-free and -Wuseless-cast
	from here....
	(Warning Options): ...to here.  Minor copy-editing to fix typo
	and grammar.