rs6000: Use pointers in bswap testcases

rs6000: Use pointers in bswap testcases

Currently these bswap testcases use global variables, which causes
problems with -m32: the memory access is a D-form access, and when
combine tries to combine that with the bswap it tries a D-form store
with byte reverse.  That instruction does not exist, and since combine
started with only two insns here it will not try splitting this.

This should be improved, but it is not what this test is testing, and
the "load" case already uses a pointer, so let's do that for the store
case as well.

	* gcc.target/powerpc/bswap16.c: Use a pointer instead of a global for
	the "store" test as well.
	* gcc.target/powerpc/bswap32.c: Ditto.

From-SVN: r269771