classes: add go112.bbclass to fix build with go 1.12

Fixed the issue:
| build cache is disabled by GOCACHE=off, but required as of Go 1.12

Issue-ID: INF-4
Signed-off-by: Jackie Huang <jackie.huang@windriver.com>
Change-Id: I6c87014428194382bb68d09119ddd670437d55c5
diff --git a/meta-oran/classes/go112.bbclass b/meta-oran/classes/go112.bbclass
new file mode 100644
index 0000000..15fa53a
--- /dev/null
+++ b/meta-oran/classes/go112.bbclass
@@ -0,0 +1,7 @@
+#
+# Copyright (C) 2019 Wind River Systems, Inc.
+#
+
+do_compile_prepend() {
+    unset GOCACHE
+}