Fix most GCC warnings during build. Only -Wattribute left.

llvm-svn: 246280
diff --git a/libcxx/include/system_error b/libcxx/include/system_error
index 66bf6d6..134bb32 100644
--- a/libcxx/include/system_error
+++ b/libcxx/include/system_error
@@ -371,7 +371,7 @@
     error_category() _NOEXCEPT;
 #else
     _LIBCPP_ALWAYS_INLINE
-    _LIBCPP_CONSTEXPR_AFTER_CXX11 error_category() _NOEXCEPT _LIBCPP_DEFAULT;
+    _LIBCPP_CONSTEXPR_AFTER_CXX11 error_category() _NOEXCEPT _LIBCPP_DEFAULT
 #endif
 private:
     error_category(const error_category&);// = delete;