More '#ifdef ASM_OUTPUT_DEF' -> 'if (TARGET_SUPPORTS_ALIASES)' etc.

More '#ifdef ASM_OUTPUT_DEF' -> 'if (TARGET_SUPPORTS_ALIASES)' etc.

Per commit a8b522b483ebb8c972ecfde8779a7a6ec16aecd6 (Subversion r251048)
"Introduce TARGET_SUPPORTS_ALIASES", there is the idea that a back end may or
may not provide symbol aliasing support ('TARGET_SUPPORTS_ALIASES') independent
of '#ifdef ASM_OUTPUT_DEF', and in particular, depending not just on static but
instead on dynamic (run-time) configuration.  There did remain a few instances
where we currently still assume that from '#ifdef ASM_OUTPUT_DEF' follows
'TARGET_SUPPORTS_ALIASES'.  Change these to 'if (TARGET_SUPPORTS_ALIASES)',
similarly, or 'gcc_checking_assert (TARGET_SUPPORTS_ALIASES);'.

	gcc/
	* ipa-icf.cc (sem_item::target_supports_symbol_aliases_p):
	'gcc_checking_assert (TARGET_SUPPORTS_ALIASES);' before
	'return true;'.
	* ipa-visibility.cc (function_and_variable_visibility): Change
	'#ifdef ASM_OUTPUT_DEF' to 'if (TARGET_SUPPORTS_ALIASES)'.
	* varasm.cc (output_constant_pool_contents)
	[#ifdef ASM_OUTPUT_DEF]:
	'gcc_checking_assert (TARGET_SUPPORTS_ALIASES);'.
	(do_assemble_alias) [#ifdef ASM_OUTPUT_DEF]:
	'if (!TARGET_SUPPORTS_ALIASES)',
	'gcc_checking_assert (seen_error ());'.
	(assemble_alias): Change '#if !defined (ASM_OUTPUT_DEF)' to
	'if (!TARGET_SUPPORTS_ALIASES)'.
	(default_asm_output_anchor):
	'gcc_checking_assert (TARGET_SUPPORTS_ALIASES);'.