Allow linker to compile with -DLINKER_DEBUG=1

Change-Id: I27e734048cbcb9ed936369115582b3c734de1280

linker/linker_debug.h

@@ -61,6 +61,11 @@
  */
 #if LINKER_DEBUG
 #include "linker_format.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 extern int debug_verbosity;
 #if LINKER_DEBUG_TO_LOG
 extern int format_log(int, const char *, const char *, ...);
@@ -75,6 +80,11 @@ extern int format_fd(int, const char *, ...);
         if (debug_verbosity > (v)) format_fd(1, x);  \
     } while (0)
 #endif /* !LINKER_DEBUG_TO_LOG */
+
+#ifdef __cplusplus
+};
+#endif
+
 #else /* !LINKER_DEBUG */
 #define _PRINTVF(v,f,x...)   do {} while(0)
 #endif /* LINKER_DEBUG */