Fix mac build

"errno.h" doesn't get included on mac so we need to do it explicitely.

system/core/libnativebridge/tests/CodeCacheExists_test.cpp:30:15: error:
use of undeclared identifier 'ENOENT'
      ASSERT_EQ(ENOENT, errno);

(cherry picked from commit bcd1a834d4)

Change-Id: Ib894e3a3912a943c61787461f127e4b11aacf212

libnativebridge/tests/CodeCacheCreate_test.cpp

@@ -16,6 +16,7 @@
 
 #include "NativeBridgeTest.h"
 
+#include <errno.h>
 #include <sys/stat.h>
 #include <unistd.h>
 

libnativebridge/tests/CodeCacheExists_test.cpp

@@ -16,6 +16,7 @@
 
 #include "NativeBridgeTest.h"
 
+#include <errno.h>
 #include <sys/stat.h>
 #include <unistd.h>