Fix PR gas/22738 (.dc.a directive has wrong size on SPARC 64-bit).

Fix PR gas/22738 (.dc.a directive has wrong size on SPARC 64-bit).

The .dc.a directive has wrong size (32 bits) on SPARC 64-bit because
the assembler sets the correct BFD architecture only at the very end
of the processing and it's too late for the directive.  It's fixed by
defining TARGET_MACH and making it return a sensible default value.

gas/
	* config/tc-sparc.h (sparc_mach): Declare.
	(TARGET_MACH): Define to above.
	* config/tc-sparc.c (sparc_mach): New function.
	(sparc_md_end): Minor tweak.
ld/
	* testsuite/ld-elf/pr22450.d: Remove reference to SPARC64.