merge in jb-mr0-release history after reset to jb-dev

Since linker is built with -fvisibility=hidden rtld_db_dlactivity()
if hidden from gdb.  Unhide it otherwise gdb may not know linker
activity and rescan solib

Change-Id: Ia8cd8d9738c6ea5696ba2ef0ebf2cf783f9ca70a

linker/linker.c

@@ -159,7 +159,7 @@ const char *linker_get_error(void)
  * This function is an empty stub where GDB locates a breakpoint to get notified
  * about linker activity.
  */
-extern void __attribute__((noinline)) rtld_db_dlactivity(void);
+extern void __attribute__((noinline)) __attribute__((visibility("default"))) rtld_db_dlactivity(void);
 
 static struct r_debug _r_debug = {1, NULL, &rtld_db_dlactivity,
                                   RT_CONSISTENT, 0};

linker/rt.c

@@ -28,9 +28,9 @@
 
 /*
  * This function is an empty stub where GDB locates a breakpoint to get notified
- * about linker activity.
+ * about linker activity.  It canʼt be inlined away, canʼt be hidden.
  */
-void __attribute__((noinline)) rtld_db_dlactivity(void)
+void __attribute__((noinline)) __attribute__((visibility("default"))) rtld_db_dlactivity(void)
 {
 }