compiler: write barrier check nil-check policy tweak

Tweak the recipe for generating writeBarrier loads to insure that the
dereference expr is marked as not requiring a nil check (not needed
for gccgo, but needed for gollvm).

Fixes https://gcc.gnu.org/PR89368

Change-Id: If057f1359c3e3e78612abc33d605d9e6908ec21c
Reviewed-on: https://go-review.googlesource.com/c/162904
Reviewed-by: Ian Lance Taylor <iant@golang.org>
1 file changed