runtime: provide and use a GO_PPC64X_HAS_FUNCDESC define
Rather than implying that all ppc64 GOARCHs use function descriptors,
provide a define for platforms that make use of function descriptors.
Condition on GO_PPC64X_HAS_FUNCDESC when choosing whether or not
to load the entry address from the first slot of the function
descriptor.
Updates #56001.
Change-Id: I9cdc788f2de70a1262c17d8485b555383d1374b5
Reviewed-on: https://go-review.googlesource.com/c/go/+/476117 Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Run-TryBot: Joel Sing <joel@sing.id.au> Reviewed-by: Lynn Boger <laboger@linux.vnet.ibm.com>
TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Cherry Mui <cherryyz@google.com>