_content/doc: add backwards compatibility note for ppc64/linux

For golang/go#78779

Change-Id: I2a618c40c428230f0d6d30f1d4f93e15aa3a87f2
Reviewed-on: https://go-review.googlesource.com/c/website/+/786083
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Mark Freeman <markfreeman@google.com>
LUCI-TryBot-Result: golang-scoped@luci-project-accounts.iam.gserviceaccount.com <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
diff --git a/_content/doc/go1.27.md b/_content/doc/go1.27.md
index 4c6fdbc..ddf397b 100644
--- a/_content/doc/go1.27.md
+++ b/_content/doc/go1.27.md
@@ -426,6 +426,13 @@
 has no effect for those building and running pure Go
 binaries.
 
+On ppc64, for maximum backward compatibility, existing users
+should explicitly disable cgo, external linking, and use the
+default build mode. That is, set `CGO_ENABLED=0` in the
+environment, and pass the option `-ldflags="-linkmode=internal"`
+to go build and similar. Linux ELFv2 support was added in
+3.13, RHEL7 backported this support to its 3.10 kernel.
+
 On ppc64, external linking, cgo, and PIE binaries are now
 supported. Using these features requires an ELFv2 compatible
 runtime (libc, kernel, and all linked and loaded libraries).
@@ -436,10 +443,6 @@
 Some of them may not need any documentation or may be false
 positives from automation.
 
-### TODO: CL 734540 has a RELNOTE comment without a suggested text (from RELNOTE comment in [/cl/734540](/cl/734540))
-
-- `all: switch linux-ppc64 target to ELFv2 ABI`
-
 ### TODO: CL 751260 has a RELNOTE comment without a suggested text (from RELNOTE comment in [/cl/751260](/cl/751260))
 
 - `cmd/link: add -macos and -macsdk flags to set LC_BUILD_VERSION`