MIPS/LD/testsuite: Fix MIPS16 interlinking test IRIX 6 regressions

MIPS/LD/testsuite: Fix MIPS16 interlinking test IRIX 6 regressions

IRIX 6 does not have MIPS16 stub section support in its n32 linker
scripts, causing such input sections to be propagated to the respective
output sections rather than `.text', causing dump pattern mismatches.

Expect IRIX 6 to fail with n32 testing then, removing this regression:

mips-sgi-irix6  -FAIL: MIPS16 interlinking for local functions 1 (n32)

We may choose to update IRIX 6 n32 linker scripts sometime, as it seems
a harmless change.

	ld/
	* testsuite/ld-mips-elf/mips-elf.exp: Expect IRIX 6 to fail with
	n32 `mips16-local-stubs-1' testing.