Default to disabling the linker warnings about execstack and RWX segments if the target is the HPPA architecture.

	PR 29263
	* configure.ac (ac_default_ld_warn_execstack): Default to 'no' for
	HPPA targets.
	(ac_default_ld_warn_rwx_segments): Likewise.
	* configure: Regenerate.
	* testsuite/ld-elf/elf.exp: Add the --warn-execstack command line
	option to the command line when running execstack tests for the
	HPPA target.