Use extern "C" rather than BEGIN/END_DECLS.

For compatibility with Trusty.  I'll probably revert this later after I
find a proper fix for Trusty.

Change-Id: I49b4ae55251398eec2a6633e09bbc468f16a4d14
diff --git a/include/hardware/keymaster_defs.h b/include/hardware/keymaster_defs.h
index e7ef5b5..664d3a7 100644
--- a/include/hardware/keymaster_defs.h
+++ b/include/hardware/keymaster_defs.h
@@ -21,7 +21,9 @@
 #include <stdlib.h>
 #include <string.h>
 
-__BEGIN_DECLS
+#ifndef __cplusplus
+extern "C" {
+#endif  // __cplusplus
 
 /**
  * Authorization tags each have an associated type.  This enumeration facilitates tagging each with
@@ -546,6 +548,8 @@
     }
 }
 
-__END_DECLS
+#ifndef __cplusplus
+}  // extern "C"
+#endif  // __cplusplus
 
 #endif  // ANDROID_HARDWARE_KEYMASTER_DEFS_H