cmd/go/testdata/script: add darwin skips for selected buildrepro tests

Skip two build reproducibility tests (build_issue48319 and
build_plugin_reproducible) on Darwin if GO_BUILDER_NAME is set until
issue 64947 can be resolved; on the LUCI darwin longtest builder the
more contemporary version of Xcode is doing things that are unfriendly
to Go's build reproducibility.

For #64947.

Change-Id: Iebd433ad6dfeb84b6504ae9355231d897d8ae174
Reviewed-on: https://go-review.googlesource.com/c/go/+/565376
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

src/cmd/go/testdata/script/build_issue48319.txt

@@ -4,6 +4,13 @@
 [short] skip
 [!cgo] skip
 
+# This test has problems when run on the LUCI darwin longtest builder,
+# which uses a more contemporary Xcode version that is unfriendly to
+# reproducible builds (see issue #64947 for the gory details). Note
+# that individual developers running "go test cmd/go" on Darwin may
+# still run into failures depending on their Xcode version.
+[GOOS:darwin] [go-builder] skip
+
 # This test is sensitive to cache invalidation,
 # so use a separate build cache that we can control.
 env GOCACHE=$WORK/gocache

src/cmd/go/testdata/script/build_plugin_reproducible.txt

@@ -2,6 +2,13 @@
 [short] skip
 [!cgo] skip '-buildmode=plugin requires external linking'
 
+# This test has problems when run on the LUCI darwin longtest builder,
+# which uses a more contemporary Xcode version that is unfriendly to
+# reproducible builds (see issue #64947 for the gory details). Note
+# that individual developers running "go test cmd/go" on Darwin may
+# still run into failures depending on their Xcode version.
+[GOOS:darwin] [go-builder] skip
+
 go build -trimpath -buildvcs=false -buildmode=plugin -o a.so main.go
 go build -trimpath -buildvcs=false -buildmode=plugin -o b.so main.go
 cmp -q a.so b.so