XFail TestMemoryFind on 32-bit architectures

the test fails for a very prosaic reason: `(const char *)0x1000` returns "4096" on x86_64 and
"1000" (without the "0x") on i386. I haven't tried other 32-bit arches, but I am guessing the
behaviour is the same. XFAIL until someone can get a chance to look at this.

llvm-svn: 280344