Add extern "C" to all the adb headers.

Change-Id: Iaefa3e18d6ee2e065eb97271a796613b2a8e7d6e
diff --git a/adb/adb.h b/adb/adb.h
index 6ac4731..600bdd5 100644
--- a/adb/adb.h
+++ b/adb/adb.h
@@ -23,6 +23,10 @@
 #include "fdevent.h"
 #include "transport.h"  /* readx(), writex() */
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 #define MAX_PAYLOAD 4096
 
 #define A_SYNC 0x434e5953
@@ -420,4 +424,8 @@
 int sendfailmsg(int fd, const char *reason);
 int handle_host_request(char *service, transport_type ttype, char* serial, int reply_fd, asocket *s);
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif