ARM: fix -masm-syntax-unified (PR88648)

ARM: fix -masm-syntax-unified (PR88648)

This allows to use unified asm syntax when compiling for the
ARM instruction. This matches documentation and seems what the
initial patch was intended doing when the flag got added.

2019-01-10  Stefan Agner  <stefan@agner.ch>

	PR target/88648
	* config/arm/arm.c (arm_option_override_internal): Force
	opts->x_inline_asm_unified to true only if TARGET_THUMB2_P.

	* gcc.target/arm/pr88648-asm-syntax-unified.c: Add test to
	check if -masm-syntax-unified gets applied properly.

From-SVN: r267804