Make library/header paths visible to cmd/go script tests, which is necessary for
cgo/gccgo tests to work correctly

diff --git a/src/cmd/go/script_test.go b/src/cmd/go/script_test.go
index dfaa40548e..9d0f0e9bcd 100644
--- a/src/cmd/go/script_test.go
+++ b/src/cmd/go/script_test.go
@@ -100,6 +100,10 @@ const (
 var extraEnvKeys = []string{
 	"SYSTEMROOT",         // must be preserved on Windows to find DLLs; golang.org/issue/25210
 	"WINDIR",             // must be preserved on Windows to be able to run PowerShell command; golang.org/issue/30711
+	"CPATH",
+	"C_INCLUDE_PATH",
+	"CPLUS_INCLUDE_PATH",
+	"LIBRARY_PATH",
 	"LD_LIBRARY_PATH",    // must be preserved on Unix systems to find shared libraries
 	"CC",                 // don't lose user settings when invoking cgo
 	"GO_TESTING_GOTOOLS", // for gccgo testing