[release-branch.go1.15] cmd/go: permit CGO_LDFLAGS to appear in //go:ldflag

For #42565
Fixes #42567

Change-Id: If7cf39905d124dbd54dfac6a53ee38270498efed
Reviewed-on: https://go-review.googlesource.com/c/go/+/269818
Trust: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>
(cherry picked from commit 782cf560db4c919790fdb476d1bbe18e5ddf5ffd)
Reviewed-on: https://go-review.googlesource.com/c/go/+/270137

1 files changed, 44 insertions, 0 deletions

diff --git a/src/cmd/go/testdata/script/ldflag.txt b/src/cmd/go/testdata/script/ldflag.txt
new file mode 100644
index 0000000000..6ceb33bb70
--- /dev/null
+++ b/src/cmd/go/testdata/script/ldflag.txt
@@ -0,0 +1,44 @@
+# Issue #42565
+
+[!cgo] skip
+
+# We can't build package bad, which uses #cgo LDFLAGS.
+cd bad
+! go build
+stderr no-such-warning
+
+# We can build package ok with the same flags in CGO_LDFLAGS.
+env CGO_LDFLAGS=-Wno-such-warning -Wno-unknown-warning-option
+cd ../ok
+go build
+
+# Build a main program that actually uses LDFLAGS.
+cd ..
+go build -ldflags=-v
+
+# Because we passed -v the Go linker should print the external linker
+# command which should include the flag we passed in CGO_LDFLAGS.
+stderr no-such-warning
+
+-- go.mod --
+module ldflag
+
+-- bad/bad.go --
+package bad
+
+// #cgo LDFLAGS: -Wno-such-warning -Wno-unknown-warning
+import "C"
+
+func F() {}
+-- ok/ok.go --
+package ok
+
+import "C"
+
+func F() {}
+-- main.go --
+package main
+
+import _ "ldflag/ok"
+
+func main() {}