Add extern "C" to all the adb headers.

Change-Id: Iaefa3e18d6ee2e065eb97271a796613b2a8e7d6e
diff --git a/adb/adb_trace.h b/adb/adb_trace.h
index b8a2f4c..69b6c69 100644
--- a/adb/adb_trace.h
+++ b/adb/adb_trace.h
@@ -21,6 +21,10 @@
 #include <android/log.h>
 #endif
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 /* define ADB_TRACE to 1 to enable tracing support, or 0 to disable it */
 #define  ADB_TRACE    1
 
@@ -142,4 +146,8 @@
 #  define  ADB_TRACING     0
 #endif /* ADB_TRACE */
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif /* __ADB_TRACE_H */