MIPS/GAS: Fix `.option picX' handling with relaxation

MIPS/GAS: Fix `.option picX' handling with relaxation

Correct the handling of `.option pic0' and `.option pic2' GAS pseudo-ops
in relaxation and use the setting of `mips_pic' (which these directives
control) as at the time a relaxed frag has been created rather than the
final `mips_pic' setting at the end of the source file processed.

To do so record whether `mips_pic' is NO_PIC or not in the frag itself
and use this information throughout relaxation instead of `mips_pic' to
decide which of NO_PIC or SVR4_PIC to produce machine code for, fixing
code generation and removing a possible fatal failure reproducible with:

$ as -32 --relax-branch -o option-pic-relax-3.o option-pic-relax-3.s
option-pic-relax-3.s: Assembler messages:
option-pic-relax-3.s:7: Warning: relaxed out-of-range branch into a jump
option-pic-relax-3.s: Internal error in cvt_frag_to_fill at .../gas/write.c:490.
Please report this bug.
$

using the test source included, due to a buffer overrun in filling the
variable part of a frag.

Likewise use the `fx_tcbit2' flag of a BFD_RELOC_16_PCREL_S2 fixup to
handle the simple case of substituting an out of range unconditional
branch with an equivalent absolute jump in NO_PIC code.

Retain the current way of VXWORKS_PIC use, which commit 41a1578ed17c
("MIPS/GAS: Sanitize `.option picX' pseudo-op") has forbidden the use of
`.option picX' with.

	gas/
	* config/tc-mips.c (RELAX_ENCODE): Add `PIC' flag.
	(RELAX_PIC): New macro.
	(RELAX_USE_SECOND, RELAX_SECOND_LONGER, RELAX_NOMACRO)
	(RELAX_DELAY_SLOT, RELAX_DELAY_SLOT_16BIT)
	(RELAX_DELAY_SLOT_SIZE_FIRST, RELAX_DELAY_SLOT_SIZE_SECOND):
	Shift bits.
	(RELAX_BRANCH_ENCODE): Add `pic' flag.
	(RELAX_BRANCH_UNCOND, RELAX_BRANCH_LIKELY, RELAX_BRANCH_LINK)
	(RELAX_BRANCH_TOOFAR): Shift bits.
	(RELAX_BRANCH_PIC): New macro.
	(RELAX_MICROMIPS_ENCODE): Add `pic' flag.
	(RELAX_MICROMIPS_PIC): New macro.
	(RELAX_MICROMIPS_UNCOND, RELAX_MICROMIPS_COMPACT)
	(RELAX_MICROMIPS_LINK, RELAX_MICROMIPS_NODS)
	(RELAX_MICROMIPS_RELAX32): Shift bits.
	(relax_close_frag): Pass `mips_pic' setting to RELAX_ENCODE.
	(append_insn): Pass `mips_pic' setting to RELAX_BRANCH_ENCODE
	and RELAX_MICROMIPS_ENCODE, and record it in `fx_tcbit2' of the
	first fixup created.
	(md_apply_fix) <BFD_RELOC_16_PCREL_S2>: Use `fx_tcbit2' of the
	fixup processed rather than `mips_pic' in choosing to relax an
	out of range branch to a jump.
	(relaxed_branch_length): Use the `pic' flag of the relaxed frag
	rather than `mips_pic'.
	(relaxed_micromips_32bit_branch_length): Likewise.
	(md_estimate_size_before_relax): Likewise.
	(md_convert_frag): Likewise.

	* testsuite/gas/mips/option-pic-relax-0.d: New test.
	* testsuite/gas/mips/option-pic-relax-1.d: New test.
	* testsuite/gas/mips/option-pic-relax-2.d: New test.
	* testsuite/gas/mips/option-pic-relax-3.d: New test.
	* testsuite/gas/mips/option-pic-relax-3a.d: New test.
	* testsuite/gas/mips/option-pic-relax-4.d: New test.
	* testsuite/gas/mips/option-pic-relax-5.d: New test.
	* testsuite/gas/mips/option-pic-relax-2.l: New stderr output.
	* testsuite/gas/mips/option-pic-relax-3.l: New stderr output.
	* testsuite/gas/mips/option-pic-relax-4.l: New stderr output.
	* testsuite/gas/mips/option-pic-relax-5.l: New stderr output.
	* testsuite/gas/mips/option-pic-relax-0.s: New test source.
	* testsuite/gas/mips/option-pic-relax-1.s: New test source.
	* testsuite/gas/mips/option-pic-relax-2.s: New test source.
	* testsuite/gas/mips/option-pic-relax-3.s: New test source.
	* testsuite/gas/mips/option-pic-relax-4.s: New test source.
	* testsuite/gas/mips/option-pic-relax-5.s: New test source.
	* testsuite/gas/mips/mips.exp: Run the new tests.