build: Unify 32 and 64-bit assembler handling

build: Unify 32 and 64-bit assembler handling

gcc/configure.ac uses various ways to handle differences between GNU as
and Solaris as assembler options and syntax.

This patch unifies all those, setting gcc_cv_as_flags, as_32_opt, and
as_64_opt once in acinclude.m4 (gcc_GAS_FLAGS) and using the result
everywhere.  Besides, handling Solaris as syntax differences from GNU as
is done in a more readable way.

Bootstrapped without regressions on i386-pc-solaris2.11,
x86_64-pc-solaris2.11, x86_64-pc-linux-gnu, x86_64-unknown-freebsd14.3,
and x86_64-apple-darwin21.6.0.

	gcc:
	* acinclude.m4 (gcc_cv_as_flags) Provide Solaris settings.
	Apply Linux/x86 gas settings on all x86 gas targets, too.
	(as_32_opt, as_64_opt): Set on all x86 gas targets.
	* configure.ac: Consistenly use as_32_opt, as_64_opt instead of
	as_ix86_gas_{32,64}_opt or hardcoded --64.
	<sparc*-*-*>: Simplify setting TLS test code.
	* configure: Regenerate.