Correct a MIPS16 relocation handling regression in GAS introduced with:

commit 177b4a6a
Author: Alexandre Oliva <aoliva@redhat.com>
Date:   Mon Mar 18 18:56:18 2002 +0000

discussed at <https://sourceware.org/ml/binutils/2002-03/msg00345.html>,
which removed a preparatory call to `mips16_extended_frag' previously
made from `md_estimate_size_before_relax'.  As a result the function is
never called with its `sec' parameter non-NULL and consequently all the
unsupported relocation checks within are dead and never trigger, causing
any unhandled relocations to silently resolve to 0.  Unfortunately there
was no sufficient test suite coverage back then to catch this.

Remove all dead code then, and all the associated comments.  Update the
remaining call to `mips16_extended_frag' from `mips_relax_frag' to pass
the relocation section as the `sec' parameter and use it to mark frags
which require an external relocation, as extended.  Finally handle any
outstanding MIPS16 relocations in `md_convert_frag' and report an error
since we don't support any except with percent operators.

	gas/
	* config/tc-mips.c (append_insn): Use any `O_symbol' expression
	unchanged with relaxed MIPS16 instructions.
	(mips16_extended_frag): Adjust accordingly.  Return 1 right
	away if a relocation will be required for the symbol requested.
	Remove dead first relaxation pass code.
	(mips_relax_frag): Pass `sec' down to `mips16_extended_frag'.
	(md_convert_frag): Adjust symbol value calculation.  Raise an
	error if a relocation is required for the symbol requested.
	* testsuite/gas/mips/mips16@relax-swap3.d: Remove dump patterns,
	add error output.
	* testsuite/gas/mips/mips16@relax-swap3.l: New error output.
	* testsuite/gas/mips/mips16-pcrel-relax-0.d: New test.
	* testsuite/gas/mips/mips16-pcrel-relax-1.d: New test.
	* testsuite/gas/mips/mips16-pcrel-relax-2.d: New test.
	* testsuite/gas/mips/mips16-pcrel-relax-3.d: New test.
	* testsuite/gas/mips/mips16-pcrel-reloc-0.d: New test.
	* testsuite/gas/mips/mips16-pcrel-reloc-1.d: New test.
	* testsuite/gas/mips/mips16-pcrel-reloc-2.d: New test.
	* testsuite/gas/mips/mips16-pcrel-reloc-3.d: New test.
	* testsuite/gas/mips/mips16-pcrel-reloc-4.d: New test.
	* testsuite/gas/mips/mips16-pcrel-reloc-5.d: New test.
	* testsuite/gas/mips/mips16-pcrel-reloc-6.d: New test.
	* testsuite/gas/mips/mips16-pcrel-reloc-7.d: New test.
	* testsuite/gas/mips/mips16-pcrel-addend-0.d: New test.
	* testsuite/gas/mips/mips16-pcrel-addend-1.d: New test.
	* testsuite/gas/mips/mips16-pcrel-addend-2.d: New test.
	* testsuite/gas/mips/mips16-pcrel-addend-3.d: New test.
	* testsuite/gas/mips/mips16-pcrel-absolute.d: New test.
	* testsuite/gas/mips/mips16-branch-reloc-0.d: New test.
	* testsuite/gas/mips/mips16-branch-reloc-1.d: New test.
	* testsuite/gas/mips/mips16-branch-reloc-2.d: New test.
	* testsuite/gas/mips/mips16-branch-reloc-3.d: New test.
	* testsuite/gas/mips/mips16-branch-addend-0.d: New test.
	* testsuite/gas/mips/mips16-branch-addend-1.d: New test.
	* testsuite/gas/mips/mips16-branch-addend-2.d: New test.
	* testsuite/gas/mips/mips16-branch-addend-3.d: New test.
	* testsuite/gas/mips/mips16-branch-absolute.d: New test.
	* testsuite/gas/mips/mips16-absolute-reloc-0.d: New test.
	* testsuite/gas/mips/mips16-absolute-reloc-1.d: New test.
	* testsuite/gas/mips/mips16-absolute-reloc-2.d: New test.
	* testsuite/gas/mips/mips16-absolute-reloc-3.d: New test.
	* testsuite/gas/mips/mips16-pcrel-reloc-2.l: New error output.
	* testsuite/gas/mips/mips16-pcrel-reloc-3.l: New error output.
	* testsuite/gas/mips/mips16-pcrel-reloc-6.l: New error output.
	* testsuite/gas/mips/mips16-pcrel-reloc-7.l: New error output.
	* testsuite/gas/mips/mips16-pcrel-addend-2.l: New error output.
	* testsuite/gas/mips/mips16-pcrel-addend-3.l: New error output.
	* testsuite/gas/mips/mips16-pcrel-absolute.l: New error output.
	* testsuite/gas/mips/mips16-branch-reloc-2.l: New error output.
	* testsuite/gas/mips/mips16-branch-reloc-3.l: New error output.
	* testsuite/gas/mips/mips16-branch-addend-2.l: New error output.
	* testsuite/gas/mips/mips16-branch-addend-3.l: New error output.
	* testsuite/gas/mips/mips16-branch-absolute.l: New error output.
	* testsuite/gas/mips/mips16-absolute-reloc-2.l: New error output.
	* testsuite/gas/mips/mips16-absolute-reloc-3.l: New error output.
	* testsuite/gas/mips/mips16-pcrel-relax-0.s: New test source.
	* testsuite/gas/mips/mips16-pcrel-relax-2.s: New test source.
	* testsuite/gas/mips/mips16-pcrel-reloc-0.s: New test source.
	* testsuite/gas/mips/mips16-pcrel-reloc-1.s: New test source.
	* testsuite/gas/mips/mips16-pcrel-reloc-2.s: New test source.
	* testsuite/gas/mips/mips16-pcrel-reloc-3.s: New test source.
	* testsuite/gas/mips/mips16-pcrel-reloc-4.s: New test source.
	* testsuite/gas/mips/mips16-pcrel-reloc-5.s: New test source.
	* testsuite/gas/mips/mips16-pcrel-reloc-6.s: New test source.
	* testsuite/gas/mips/mips16-pcrel-reloc-7.s: New test source.
	* testsuite/gas/mips/mips16-pcrel-addend-0.s: New test source.
	* testsuite/gas/mips/mips16-pcrel-addend-1.s: New test source.
	* testsuite/gas/mips/mips16-pcrel-addend-2.s: New test source.
	* testsuite/gas/mips/mips16-pcrel-addend-3.s: New test source.
	* testsuite/gas/mips/mips16-pcrel-absolute.s: New test source.
	* testsuite/gas/mips/mips16-branch-reloc-0.s: New test source.
	* testsuite/gas/mips/mips16-branch-reloc-1.s: New test source.
	* testsuite/gas/mips/mips16-branch-reloc-2.s: New test source.
	* testsuite/gas/mips/mips16-branch-reloc-3.s: New test source.
	* testsuite/gas/mips/mips16-branch-addend-0.s: New test source.
	* testsuite/gas/mips/mips16-branch-addend-1.s: New test source.
	* testsuite/gas/mips/mips16-branch-addend-2.s: New test source.
	* testsuite/gas/mips/mips16-branch-addend-3.s: New test source.
	* testsuite/gas/mips/mips16-branch-absolute.s: New test source.
	* testsuite/gas/mips/mips16-absolute-reloc-0.s: New test source.
	* testsuite/gas/mips/mips16-absolute-reloc-1.s: New test source.
	* testsuite/gas/mips/mips16-absolute-reloc-2.s: New test source.
	* testsuite/gas/mips/mips16-absolute-reloc-3.s: New test source.
	* testsuite/gas/mips/mips.exp: Run the new tests.