cmd/cgo/internal/testsanitizers: avoid clang error in msan8.go

In clang 16 the option -fsanitize-memory-param-retval was turned on by
default. That option causes MSAN to issue a warning when calling a
function with an uninitialized value. The msan8 test relies on being
able to do this, in order to get uninitialized values into registers.

This CL fixes the test by adding maybe_undef attributes that tell
clang that it's OK to pass an uninitialized variable. The docs for
maybe_undef say: "Please note that this is an attribute that is used as
an internal implementation detail and not intended to be used by
external users." So this may break in the future, but it does work for now.

Fixes #64616

Change-Id: I0ac8c0520fce8c32e26d2a5efb7ae5e02461c1ce
Reviewed-on: https://go-review.googlesource.com/c/go/+/601779
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>

0 files changed, 0 insertions, 0 deletions