config/mmix/mmix.c (TARGET_ASM_OUTPUT_IDENT): Override.

config/mmix/mmix.c (TARGET_ASM_OUTPUT_IDENT): Override.

Funny that default_asm_output_ident_directive isn't the default...
Anyway, since dot-pseudos like .ident are treated as comments by
mmixal, there's nothing lost compatibilitywise by supporting it.
If mmix-knuth-mmixware had included elfos.h this'd have been the
default.  There might be enough reason to do that; relocatable objects
are ELF but (by default) links to produce mmo.  Fixes
c-c++-common/ident-1b.c and 2b in C and C++ testing.  Committed.

gcc:
	* config/mmix/mmix.c (TARGET_ASM_OUTPUT_IDENT): Override the default
	with default_asm_output_ident_directive.