Switch to C++11 style [[noreturn]].

Also remove old comment about calls to Abort getting merged. We have few
LOG(FATAL)s so merging is less of an issue. Also, recompiling with O0 and
similar will avoid the optimization and we expect that for GDB debugging.

Change-Id: I840dc6f4b8511294be0e117c634ec15b745e7be5
diff --git a/dex2oat/dex2oat.cc b/dex2oat/dex2oat.cc
index d782aeb..7be4349 100644
--- a/dex2oat/dex2oat.cc
+++ b/dex2oat/dex2oat.cc
@@ -90,8 +90,7 @@
   va_end(ap);
 }
 
-static void Usage(const char* fmt, ...) NO_RETURN;
-static void Usage(const char* fmt, ...) {
+[[noreturn]] static void Usage(const char* fmt, ...) {
   va_list ap;
   va_start(ap, fmt);
   UsageErrorV(fmt, ap);
@@ -663,7 +662,7 @@
     Message('W', message);
   }
 
-  static void Fatal(const std::string& message) NO_RETURN {
+  [[noreturn]] static void Fatal(const std::string& message) {
     Message('F', message);
     exit(1);
   }