misc/cgo/testso: don't use TLS variables on Darwin and OpenBSD.

Fix build for 10.6 Darwin builders and OpenBSD builers.

LGTM=jsing
R=golang-codereviews, dave, jsing
CC=golang-codereviews
https://golang.org/cl/67710043

misc/cgo/testso/cgoso_c.c

@@ -17,6 +17,10 @@ __declspec(dllexport) void sofunc(void);
 #else
 extern void goCallback(void);
 void setCallback(void *f) { (void)f; }
+#endif
+
+// OpenBSD and older Darwin lack TLS support
+#if !defined(__OpenBSD__) && !defined(__APPLE__)
 __thread int tlsvar = 12345;
 #endif
 

misc/cgo/testso/cgoso_unix.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build darwin dragonfly freebsd linux netbsd
+// +build dragonfly freebsd linux netbsd
 
 package cgosotest