MIPS16/GAS: Improve [32768,65535] out-of-range operand error diagnostics

MIPS16/GAS: Improve [32768,65535] out-of-range operand error diagnostics

Improve out-of-range operand error diagnostics for invalid values in the
[32768,65535] range used for a signed 16-bit immediate, making the
message consistent with that used for other invalid values, e.g.:

foo.s:1: Error: operand 2 must be an immediate expression `addiu $2,$gp,32768'
foo.s:2: Error: invalid operands `lw $2,32768($gp)'

vs:

foo.s:3: Error: operand 3 out of range `addiu $2,$gp,-32769'
foo.s:4: Error: operand 2 out of range `lw $2,-32769($gp)'

This case does not currently trigger however, for two reasons.

First, for regular MIPS and microMIPS assembly in the case of no match
caused by `match_int_operand' here, the function is always called again
from `mips_ip' via `match_insns', `match_insn' and then `match_operand'
for the same opcode table's entry with `lax_match' set to TRUE, in which
case the attempt to match succeeds and no error is issued.

Second, in the case of MIPS16 assembly no call to `match_int_operand' is
made at all for signed 16-bit immediates, because such immediates are
currently only matched with extensible instructions, and these are
handled in `match_mips16_insn' via `match_expression' directly rather
than via `match_operand'.

This will change for MIPS16 code with MIPS16e2 support introduced, where
non-extensible instructions accepting signed 16-bit immediates will be
added, so make the case work well right from the start:

foo.s:1: Error: operand 3 out of range `addiu $2,$gp,32768'
foo.s:2: Error: operand 2 out of range `lw $2,32768($gp)'

	gas/
	* config/tc-mips.c (match_int_operand): Call
	`match_out_of_range' before returning failure for 0x8000-0xffff
	values conditionally allowed.