[PowerPC] Support for R_PPC64_REL24_NOTOC calls where the caller has no TOC and the...

[PowerPC] Support for R_PPC64_REL24_NOTOC calls where the caller has no TOC and the callee is not DSO local

This patch supports the situation where caller does not have a valid TOC and
calls using the R_PPC64_REL24_NOTOC relocation and the callee is not DSO local.
In this case the call cannot be made directly since the callee may or may not
require a valid TOC pointer. As a result this situation require a PC-relative
plt stub to set up r12.

Reviewed By: sfertile, MaskRay, stefanp

Differential Revision: https://reviews.llvm.org/D83669