make md_parse_option () take a const char *

This is mostly just adding const in many places, however there are a couple
interesting things.  We need to add casts in tc-s390.c and tc-cris.c because
they have functions that assign to input_line_pointer an argument that
sometimes comes from md_parse_option.  Presumably this is safe because those
targets never pass literals to md_parse_option (), but this code should
probably be improved in the future.  Also xtensa passes the argument to strtoll
which is a rather odd function, it takes a const char * as argument and returns
a pointer into that string as a char * through an out argument, but we can work
around that by adding more variables.

gas/ChangeLog:

2016-03-29  Trevor Saunders  <tbsaunde+binutils@tbsaunde.org>

	* config/tc-aarch64.c (struct aarch64_long_option_table): Ad const
	qualifier.
	* config/tc-alpha.c (md_parse_option): Likewise.
	* config/tc-arc.c (md_parse_option): Likewise.
	* config/tc-arm.c (struct arm_long_option_table): Likewise.
	(md_parse_option): Likewise.
	* config/tc-avr.c (md_parse_option): Likewise.
	* config/tc-bfin.c (md_parse_option): Likewise.
	* config/tc-cr16.c (md_parse_option): Likewise.
	* config/tc-cris.c (s_cris_arch): Likewise.
	(md_parse_option): Likewise.
	* config/tc-crx.c (md_parse_option): Likewise.
	* config/tc-d10v.c (md_parse_option): Likewise.
	* config/tc-d30v.c (md_parse_option): Likewise.
	* config/tc-dlx.c (md_parse_option): Likewise.
	* config/tc-epiphany.c (md_parse_option): Likewise.
	* config/tc-fr30.c (md_parse_option): Likewise.
	* config/tc-frv.c (md_parse_option): Likewise.
	* config/tc-ft32.c (md_parse_option): Likewise.
	* config/tc-h8300.c (md_parse_option): Likewise.
	* config/tc-hppa.c (md_parse_option): Likewise.
	* config/tc-i370.c (md_parse_option): Likewise.
	* config/tc-i386.c (md_parse_option): Likewise.
	* config/tc-i860.c (md_parse_option): Likewise.
	* config/tc-i960.c (md_parse_option): Likewise.
	* config/tc-ia64.c (md_parse_option): Likewise.
	* config/tc-ip2k.c (md_parse_option): Likewise.
	* config/tc-iq2000.c (md_parse_option): Likewise.
	* config/tc-lm32.c (md_parse_option): Likewise.
	* config/tc-m32c.c (md_parse_option): Likewise.
	* config/tc-m32r.c (md_parse_option): Likewise.
	* config/tc-m68hc11.c (md_parse_option): Likewise.
	* config/tc-m68k.c (md_parse_option): Likewise.
	* config/tc-mcore.c (md_parse_option): Likewise.
	* config/tc-mep.c (md_parse_option): Likewise.
	* config/tc-metag.c (struct metag_long_option): Likewise.
	(md_parse_option): Likewise.
	* config/tc-microblaze.c (md_parse_option): Likewise.
	* config/tc-microblaze.h (md_parse_option): Remove prototype.
	* config/tc-mips.c (md_parse_option): Adjust.
	* config/tc-mmix.c (md_parse_option): Likewise.
	* config/tc-mn10200.c (md_parse_option): Likewise.
	* config/tc-mn10300.c (md_parse_option): Likewise.
	* config/tc-moxie.c (md_parse_option): Likewise.
	* config/tc-msp430.c (md_parse_option): Likewise.
	* config/tc-mt.c (md_parse_option): Likewise.
		* config/tc-nds32.c (md_parse_option): Likewise.
		* config/tc-nds32.h (nds32_parse_option): Likewise.
	* config/tc-nios2.c (md_parse_option): Likewise.
	* config/tc-ns32k.c (md_parse_option): Likewise.
	* config/tc-or1k.c (md_parse_option): Likewise.
	* config/tc-pdp11.c (md_parse_option): Likewise.
	* config/tc-pj.c (md_parse_option): Likewise.
	* config/tc-ppc.c (md_parse_option): Likewise.
	* config/tc-rl78.c (md_parse_option): Likewise.
	* config/tc-rx.c (md_parse_option): Likewise.
	* config/tc-s390.c (s390_parse_cpu): Likewise.
	* config/tc-score.c (md_parse_option): Likewise.
	* config/tc-sh.c (md_parse_option): Likewise.
	* config/tc-sparc.c (md_parse_option): Likewise.
	* config/tc-spu.c (md_parse_option): Likewise.
	* config/tc-tic30.c (md_parse_option): Likewise.
	* config/tc-tic4x.c (md_parse_option): Likewise.
	* config/tc-tic54x.c (md_parse_option): Likewise.
	* config/tc-tic6x.c (md_parse_option): Likewise.
	* config/tc-tilegx.c (md_parse_option): Likewise.
	* config/tc-tilepro.c (md_parse_option): Likewise.
	* config/tc-v850.c (md_parse_option): Likewise.
	* config/tc-vax.c (md_parse_option): Likewise.
	* config/tc-visium.c (struct visium_long_option_table): Likewise.
	* config/tc-xc16x.c (md_parse_option): Likewise.
	* config/tc-xgate.c (md_parse_option): Likewise.
	* config/tc-xstormy16.c (md_parse_option): Likewise.
	* config/tc-xtensa.c (md_parse_option): Likewise.
	* config/tc-z80.c (md_parse_option): Likewise.
	* config/tc-z8k.c (md_parse_option): Likewise.
	* tc.h (md_parse_option): Likewise.

gas/config/tc-tic4x.c

@@ -2710,7 +2710,7 @@ md_estimate_size_before_relax (fragS *fragP ATTRIBUTE_UNUSED,
 
 
 int
-md_parse_option (int c, char *arg)
+md_parse_option (int c, const char *arg)
 {
   switch (c)
     {