MultiJITTest.cpp: Tweak getPointerToNamedFunction() to be aware of also Windows x64.

In import thunk, jmp is:
  - On x86, 0xFF 0x25 [disp32].
  - On x64, 0xFF 0x25 [pcrel32].

See also my r144178.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@203523 91177308-0d34-0410-b5e6-96231b3b80d8