rs6000: vec-rotate-*.c fixes

rs6000: vec-rotate-*.c fixes

This fixes two minor problems with the new testcases.  The first is
that almost all other tests, including all vec* tests, for powerpc use
names with dashes, not underscores.  The more important one is the the
vec-rotate-1.c and vec-rotate-3.c tests need the -maltivec flag.

gcc/testsuite/
	* gcc.target/powerpc/vec_rotate-1.c: Rename to ...
	* gcc.target/powerpc/vec-rotate-1.c: ... this.  Add -maltivec option.
	* gcc.target/powerpc/vec_rotate-2.c: Rename to ...
	* gcc.target/powerpc/vec-rotate-2.c: ... this.
	* gcc.target/powerpc/vec_rotate-3.c: Rename to ...
	* gcc.target/powerpc/vec-rotate-3.c: ... this.  Add -maltivec option.
	* gcc.target/powerpc/vec_rotate-4.c: Rename to ...
	* gcc.target/powerpc/vec-rotate-4.c: ... this.

From-SVN: r274239