MIPS/GAS: Use non-zero frag offset directly in PIC branch relaxation

MIPS/GAS: Use non-zero frag offset directly in PIC branch relaxation

Use frag symbols with a non-zero offset directly in `fix_new_exp' calls
made in PIC branch relaxation.  There is no need here to make a helper
symbol to hold the result of a `symbol+offset' calculation requested as
only branches to local symbols are relaxed and in this case the LO16
part of the PIC address load sequence will have the offset accounted for
in calculation against the local GOT entry retrieved as the GOT16 high
part.  Consequently actual code produed is identical whether a helper
symbol is used or the original `symbol+offset' expression used directly.
Verify that this is indeed the case with GAS and LD tests.

	gas/
	* config/tc-mips.c (md_convert_frag): Don't make a helper
	expression symbol for `fix_new_exp' called with a non-zero
	offset.
	* testsuite/gas/mips/relax-offset.d: New test.
	* testsuite/gas/mips/mips1@relax-offset.d: New test.
	* testsuite/gas/mips/r3000@relax-offset.d: New test.
	* testsuite/gas/mips/r3900@relax-offset.d: New test.
	* testsuite/gas/mips/micromips@relax-offset.d: New test.
	* testsuite/gas/mips/relax-offset.l: New stderr output.
	* testsuite/gas/mips/relax-offset.s: New test source.
	* testsuite/gas/mips/mips.exp: Run the new tests.

	ld/
	* testsuite/ld-mips-elf/relax-offset.dd: New test.
	* testsuite/ld-mips-elf/relax-offset.gd: New test.
	* testsuite/ld-mips-elf/relax-offset-umips.dd: New test.
	* testsuite/ld-mips-elf/relax-offset-umips.gd: New test.
	* testsuite/ld-mips-elf/relax-offset.ld: New test linker script.
	* testsuite/ld-mips-elf/mips-elf.exp: Run the new tests.
	(prune_warnings): New temporary procedure.