MIPS/GAS: Correct file option settings with `.insn'

MIPS/GAS: Correct file option settings with `.insn'

This makes sure `HAVE_CODE_COMPRESSION' evaluates correctly when the
`.insn' directive is used at the beginning of a source file before any
instructions have been produced and that ELF file header's MIPS16 and
microMIPS ASE flags are set correctly in the case where no instructions
have been produced other than with the said directive.

	gas/
	* config/tc-mips.c (s_insn): Set file options.

	gas/testsuite/
	* gas/mips/insn-opts.d: New test.
	* gas/mips/insn-opts.s: New test source.
	* gas/mips/mips.exp: Run the new test.