sparc: build with -mvis on sparc32/sparcv9 and sparc64

When building for sparc32/sparcv9 or sparc64, we assume that VIS
instructions are available and use them in the sparc specific assembly
code. However we do not tell GCC to use such instructions, resulting in
slightly suboptimal code.

Fix that by passing -Wa,-Av9a -mvis to GCC.

Changelog:
	* sysdeps/sparc/sparc32/sparcv9/Makefile (sysdep-CFLAGS): Add -mvis.
	* sysdeps/sparc/sparc64/Makefile (sysdep-CFLAGS): New. Define to
	-Wa,-Av9a -mvis.