MIPS/LD/testsuite: Fix `attr-gnu-4-10' failures with IRIX targets

MIPS/LD/testsuite: Fix `attr-gnu-4-10' failures with IRIX targets

IRIX targets do not enable the production of a `.pdr' section in GAS by
default, which causes a failure with the `attr-gnu-4-10' test case due
to a difference resulting in the number and indices of sections produced
in linker output.

As the presence or absence of this section is not relevant to this test
case, just enable it unconditionally, fixing these regressions:

mips-sgi-irix5  -FAIL: ld-mips-elf/attr-gnu-4-10
mips-sgi-irix6  -FAIL: ld-mips-elf/attr-gnu-4-10

	ld/
	* testsuite/ld-mips-elf/attr-gnu-4-10.d: Add `as' tag with
	`-mpdr'.