Clean up the features.h header.

include/lol/base/private/features.h

@@ -17,17 +17,34 @@
 // ———————————————————————
 //
 
+
 // C++ compiler features detected through __has_cpp_attribute
 
-#if defined(__has_cpp_attribute) && !__has_cpp_attribute(nodiscard)
-#   error C++ compiler support for [[nodiscard]] is required (use -std=c++17?)
+#if defined(__has_cpp_attribute)
+
+#   if !__has_cpp_attribute(nodiscard)
+#       error C++ compiler support for [[nodiscard]] is required (use -std=c++17?)
+#   endif
+
+#   if !__has_cpp_attribute(fallthrough)
+#       error C++ compiler support for [[fallthrough]] is required (use -std=c++17?)
+#   endif
+
 #endif
 
-#if defined(__has_cpp_attribute) && !__has_cpp_attribute(fallthrough)
-#   error C++ compiler support for [[fallthrough]] is required (use -std=c++17?)
+
+// C++ compiler features detected through __has_feature
+
+#if defined(__has_feature)
+
+#   if !__has_feature(cxx_constexpr)
+#       error C++ compiler for constexpr is required (use -std=c++11?)
+#   endif
+
 #endif
 
-// Define some attribute macros.
+
+// Define some attribute macros
 
 #ifdef __GNUC__
 #   define lol_attr_printf_format(n, p) __attribute__((format(printf, n, p)))
@@ -35,9 +52,3 @@
 #   define lol_attr_printf_format(n, p)
 #endif
 
-#if defined(_WIN32)
-#   define LOL_ATTR_STDCALL __stdcall
-#else
-#   define LOL_ATTR_STDCALL /* */
-#endif
-