Add back LoadLibraryA fallback

src/runtime/syscall_windows_test.go

@@ -1166,7 +1166,10 @@ uintptr_t cfunc(void) {
 	dll, err = syscall.LoadDLL(name)
 	if err == nil {
 		dll.Release()
-		t.Fatalf("Bad: insecure load of DLL by base name %q before sysdll registration: %v", name, err)
+		if wantLoadLibraryEx() {
+			t.Fatalf("Bad: insecure load of DLL by base name %q before sysdll registration: %v", name, err)
+		}
+		t.Skip("insecure load of DLL, but expected")
 	}
 }
 
@@ -1212,6 +1215,24 @@ func TestBigStackCallbackSyscall(t *testing.T) {
 	}
 }
 
+// wantLoadLibraryEx reports whether we expect LoadLibraryEx to work for tests.
+func wantLoadLibraryEx() bool {
+	return testenv.Builder() != "" && (runtime.GOARCH == "amd64" || runtime.GOARCH == "386")
+}
+
+func TestLoadLibraryEx(t *testing.T) {
+	use, have, flags := runtime.LoadLibraryExStatus()
+	if use {
+		return // success.
+	}
+	if wantLoadLibraryEx() {
+		t.Fatalf("Expected LoadLibraryEx+flags to be available. (LoadLibraryEx=%v; flags=%v)",
+			have, flags)
+	}
+	t.Skipf("LoadLibraryEx not usable, but not expected. (LoadLibraryEx=%v; flags=%v)",
+		have, flags)
+}
+
 var (
 	modwinmm    = syscall.NewLazyDLL("winmm.dll")
 	modkernel32 = syscall.NewLazyDLL("kernel32.dll")