Test case trap-fnattr.cpp was failng on clang-ppc64-elf-linux2 because ppc64
sign-extends the i32 return value.
 
This is a follow-up to r241306.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@241314 91177308-0d34-0410-b5e6-96231b3b80d8