base,dev: Use the standard attribute [[noreturn]].

The [[noreturn]] attribute has been standard since c++11, and so we
don't (and haven't for a while) need to wrap it in a macro.

Change-Id: Ifba62c87c19224bb366e93ebba685a063cc750ce
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/35218
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/base/compiler.hh

@@ -46,7 +46,6 @@
 // http://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html
 
 #if defined(__GNUC__) // clang or gcc
-#  define M5_ATTR_NORETURN  __attribute__((noreturn))
 #  define M5_VAR_USED __attribute__((unused))
 #  define M5_ATTR_PACKED __attribute__ ((__packed__))
 #  define M5_NO_INLINE __attribute__ ((__noinline__))

src/base/logging.hh

@@ -121,7 +121,7 @@ class Logger
      * functions, and gcc will get mad if a function calls panic and then
      * doesn't return.
      */
-    void exit_helper() M5_ATTR_NORETURN { exit(); ::abort(); }
+    [[noreturn]] void exit_helper() { exit(); ::abort(); }
 
   protected:
     bool enabled;

src/dev/arm/gpu_nomali.hh

@@ -99,7 +99,7 @@ class NoMaliGpu : public PioDevice
      * @param err Error code from the NoMali library.
      * @param msg Message to print.
      */
-    static void gpuPanic(nomali_error_t err, const char *msg) M5_ATTR_NORETURN;
+    [[noreturn]] static void gpuPanic(nomali_error_t err, const char *msg);
     /**
      * Panic if the NoMali returned an error, do nothing otherwise.
      *