[PowerPC] Add back test case for absolute calls (removed in r211174)

As requested by Hal Finkel, this adds back a test for calls to
a known-constant function pointer value, and verifies that the
64-bit SVR4 indirect function call sequence is used.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211190 91177308-0d34-0410-b5e6-96231b3b80d8