Add more linker debug.

- Show which executable is being linked, which linker config file is
  being read, and which section in it is being used with, enabled on
  $LD_DEBUG>=1.

- Show more info to follow the dlopen() process, enabled with "dlopen"
  in the debug.ld.xxx property.

Test: Flash, boot, and look at logcat after "adb shell setprop debug.ld.all dlopen"
Bug: 120430775
Change-Id: I5441c8ced26ec0e2f04620c3d2a1ae860b792154
diff --git a/linker/linker_logger.h b/linker/linker_logger.h
index f9fc38e..fedbc05 100644
--- a/linker/linker_logger.h
+++ b/linker/linker_logger.h
@@ -49,7 +49,7 @@
   LinkerLogger() : flags_(0) { }
 
   void ResetState();
-  void Log(const char* format, ...);
+  void Log(const char* format, ...) __printflike(2, 3);
 
   uint32_t IsEnabled(uint32_t type) {
     return flags_ & type;