Merge commit d3aeac8e2 from llvm git (by Justin Hibbits)

[dim]

Summary

[PowerPC] Only use PLT annotations if using PIC relocation model

Summary:

The default static (non-PIC, non-PIE) model for 32-bit powerpc does
not use @PLT annotations and relocations in GCC.  LLVM shouldn't use
@PLT annotations either, because it breaks secure-PLT linking with
(some versions of?) GNU LD.

Update the available-externally.ll test to reflect that default mode
should be the same as the static relocation, by using the same check
prefix.

Reviewed by:    sfertile
Differential Revision: https://reviews.llvm.org/D70570

This diff needed some fuzz to apply, double-checking it via this review.

[jhibbits]

contrib/llvm-project/llvm/lib/Target/PowerPC/PPCISelLowering.cpp

4960 ↗

(On Diff #65931)

The original diff I had created, before rebasing on the giant refactor used TM.getRelocationModel(). I think this should still work, though.