PR gas/21762: MIPS: Fix .stabs directive marking labels as MIPS16

PR gas/21762: MIPS: Fix .stabs directive marking labels as MIPS16

If a .stabs directive was used before another .set directive in a MIPS
source file, s_mips_stab would call mips_mark_labels without having
initialized the mips_opts structure yet.  Fix this by calling
file_mips_check_options which will initialize mips_opts if necessary.

gas/
	PR gas/21762
	* config/tc-mips.c (s_mips_stab): Insert call to
	file_mips_check_options.
	* testsuite/gas/mips/micromips@stabs-symbol-type.d: New test.
	* testsuite/gas/mips/mips.exp: Run the new tests.
	* testsuite/gas/mips/mips16@stabs-symbol-type.d: New test.
	* testsuite/gas/mips/stabs-symbol-type.d: New test.
	* testsuite/gas/mips/stabs-symbol-type.s: New test source.