[PPC64LE] ELFv2 ABI updates for the .opd section

[PPC64LE] ELFv2 ABI updates for the .opd section
The PPC64 Little Endian (PPC64LE) target supports the ELFv2 ABI, and as
such, does not have a ".opd" section.  This is keyed off a _CALL_ELF=2
macro check.

The CALL_ELF check is not clearly documented at this time.  The basis
for usage in this patch is from the gcc thread here:
http://gcc.gnu.org/ml/gcc-patches/2013-11/msg01144.html

> Adding comment from Uli:
Looks good to me.  I think the old-style JIT doesn't really work
anyway for 64-bit, but at least with this patch LLVM will compile
and link again on a ppc64le host ...

llvm-svn: 204614