[powerpc] make test case as xfail
[powerpc] make test case as xfail

This test case which worked for a while is now failing again.  I was unable to
trace the change in status to any particular revision.


git-svn-id: c199f293c43da69278bea8e88f92242bf3aa95f7@258739 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt