Utils: Workaround missing __cpp_noexcept in clang

Clang is not defining __cpp_noexcept.

Change-Id: Icb4e2dabb413e676614a9dd478e996d587c7f5d2
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>

src/libs/utils/smallstring.h

@@ -51,6 +51,9 @@
 #endif
 
 #pragma push_macro("noexcept")
+#ifdef __clang__
+#define  __cpp_noexcept 201003
+#endif
 #ifndef __cpp_noexcept
 #define noexcept
 #endif