cmd/link: use TOC-relative trampolines on PPC64 when needed
When linking a PIE binary with the internal linker, TOC relative
relocations need to be generated. Update trampolines to indirect
call using R12 to more closely match the AIX/ELFv2 regardless of
buildmode, and work with position-indepdent code.
Likewise, update the check for offseting R_CALLPOWER relocs to
make a local call. It should be checking ldr.AttrExternal, not
ldr.IsExternal. This offset should not be adjusted for external
(non-go) object files, it is handled when ELF reloc are translated
into go relocs.
And, update trampoline tests to verify these are generated correctly
and produce a working binary using -buildmode=pie on ppc64le.
Fixes #52337
Change-Id: I8a2dea06c3237bdf0e87888b56a17b6c4c99a7de
Reviewed-on: https://go-review.googlesource.com/c/go/+/400234 Reviewed-by: Than McIntosh <thanm@google.com> Reviewed-by: Cherry Mui <cherryyz@google.com>
Run-TryBot: Paul Murphy <murp@ibm.com>
TryBot-Result: Gopher Robot <gobot@golang.org>