Change Colour constructors to be constexpr

src/blitter/common.hpp

@@ -21,7 +21,7 @@
 #endif
 
 /** Cached black value. */
-static const Colour _black_colour(0, 0, 0);
+static const constexpr Colour _black_colour(0, 0, 0);
 
 template <typename SetPixelT>
 void Blitter::DrawLineGeneric(int x1, int y1, int x2, int y2, int screen_width, int screen_height, int width, int dash, SetPixelT set_pixel)

src/gfx_type.h

@@ -180,7 +180,7 @@ union Colour {
 	 * @param b The channel for the blue colour.
 	 * @param a The channel for the alpha/transparency.
 	 */
-	Colour(uint8 r, uint8 g, uint8 b, uint8 a = 0xFF) :
+	constexpr Colour(uint8 r, uint8 g, uint8 b, uint8 a = 0xFF) :
 #if defined(__EMSCRIPTEN__)
 		r(r), g(g), b(b), a(a)
 #elif TTD_ENDIAN == TTD_BIG_ENDIAN
@@ -195,7 +195,7 @@ union Colour {
 	 * Create a new colour.
 	 * @param data The colour in the correct packed format.
 	 */
-	Colour(uint data = 0) : data(data)
+	constexpr Colour(uint data = 0) : data(data)
 	{
 	}
 };