Don't depend on "call foo" producing a X86_64_PC32.

Newer versions of the gnu assembler produce a X86_64_PLT32 for
calls. There is a change under review in llvm to do the same, so update
the tests to not depend on it.

We can still produce a R_X86_64_PC32 with ".long foo - .".

llvm-svn: 325379