re PR c/13282 (A "-Wno..." switch to turn off "missing initializer" warnings)

re PR c/13282 (A "-Wno..." switch to turn off "missing initializer" warnings)

	PR c/13282
	* c.opt (Wmissing-field-initializers): New option.
	* c-opts.c (c_common_post_options): Make -Wextra turn it on by default.
	* c-typeck.c (pop_init_level): Guard the missing field warning with
	warn_missing_field_initializers rather than extra_warnings.
	* doc/invoke.texi (-Wmissing-field-initializers): Document, moving
	some of the explanation from...
	(-Wextra): ...here.  Say that the missing field warning can be
	seperately controlled by -Wmissing-field-initializers.

cp/
	* typeck2.c (process_init_constructor): Guard the missing field warning
	with warn_missing_field_initializers rather than extra_warnings.

testsuite/
	* gcc.dg/missing-field-init-[12].c: New tests.
	* g++.dg/warn/missing-field-init-[12].C: New tests.

From-SVN: r85638