gas: Default to V8+ on 32-bit Solaris/SPARC

gas: Default to V8+ on 32-bit Solaris/SPARC

While compilers default to v8plus on 32-bit Solaris/SPARC (gcc at least
since 4.4 in 2009, cc since at least Stdio 9 in 2010), gas still uses a
sparclite default.  While this doesn't cause issue for gcc (it passes
-Av8plus as necessary), it repeatedly lead to problems in the testsuite
which has to be sprinkled with setting ASFLAGS accordingly since gas cannot
assemble the gcc output by default.

This patch switches the default to v8plus on Solaris to match gcc.
I had to introduce a new arch value, v8plus-32, matching v9-64, to allow
for this.

I cannot reliably tell if other SPARC targets are similarly affected, so
this patch restricts the change to Solaris.

Tested on sparc-sun-solaris2.11 and sparcv9-sun-solaris2.11.

2025-09-25  Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>

	gas:
	* config/tc-sparc.c (sparc_arch_table): Introduce v8plus-32.
	* configure.tgt (generic_target) <sparc-*-solaris*>: Set arch to
	v8plus-32 for 32-bit sparc.
	* testsuite/gas/sparc/v8plus.rd, testsuite/gas/sparc/v8plus.s: New
	test.
	* testsuite/gas/sparc/sparc.exp: Run it on sparc*-*-solaris2*.