libstdc++: Use __builtin_expect in __glibcxx_assert

libstdc++-v3/ChangeLog:

	* include/bits/c++config (__replacement_assert): Add noreturn
	attribute.
	(__glibcxx_assert_impl): Use __builtin_expect to hint that the
	assertion is expected to pass.

libstdc++-v3/include/bits/c++config

@@ -468,7 +468,8 @@ namespace std
 {
   // Avoid the use of assert, because we're trying to keep the <cassert>
   // include out of the mix.
-  extern "C++" inline void
+  extern "C++" _GLIBCXX_NORETURN
+  inline void
   __replacement_assert(const char* __file, int __line,
 		       const char* __function, const char* __condition)
   {
@@ -478,7 +479,7 @@ namespace std
   }
 }
 #define __glibcxx_assert_impl(_Condition)			       \
-  if (!bool(_Condition))					       \
+  if (__builtin_expect(!bool(_Condition), false))		       \
     std::__replacement_assert(__FILE__, __LINE__, __PRETTY_FUNCTION__, \
 			      #_Condition)
 #endif