ld: Extend ac_default_ld_warn_rwx_segments to all SPARC targets [PR29411]

ld: Extend ac_default_ld_warn_rwx_segments to all SPARC targets [PR29411]

As discussed in PR ld/29411, the ld warning

	[...] has a LOAD segment with RWX permissions

needs to be disabled on all SPARC targets, not just Solaris/SPARC: the
.plt section is required to be RWX by the 32-bit SPARC ELF psABI and the
64-bit SPARC Compliance Definition 2.4.1.  Given that ld only supports
SPARC ELF targets, this patch implements this.

Tested on sparc64-unknown-linux-gnu and sparc-sun-solaris2.11.

2022-07-28  Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>

	ld:
	PR ld/29411
	* configure.tgt (ac_default_ld_warn_rwx_segments): Extend to all
	sparc targets.  Expand comment.