Append target/optimize attr to the current cmdline.

Append target/optimize attr to the current cmdline.

gcc/c-family/ChangeLog:

	* c-common.c (parse_optimize_options): Combine optimize
	options with what was provided on the command line.

gcc/ChangeLog:

	* toplev.c (toplev::main): Save decoded optimization options.
	* toplev.h (save_opt_decoded_options): New.
	* doc/extend.texi: Be more clear about optimize and target
	attributes.

gcc/testsuite/ChangeLog:

	* gcc.target/i386/avx512er-vrsqrt28ps-3.c: Disable fast math.
	* gcc.target/i386/avx512er-vrsqrt28ps-5.c: Likewise.
	* gcc.target/i386/attr-optimize.c: New test.