Painter: Always optimize with -O3.

Use a GCC #pragma to always optimize the Painter code with -O3.
This code is performance critical and hotter than anything else in the
system, and this helps quite a bit.

The 2x, 3x and 4x upscaling fast paths benefit greatly from this.

SharedGraphics/Painter.cpp

@@ -9,6 +9,8 @@
 #include <stdio.h>
 #include <math.h>
 
+#pragma GCC optimize("O3")
+
 template<GraphicsBitmap::Format format = GraphicsBitmap::Format::Invalid>
 static ALWAYS_INLINE Color get_pixel(const GraphicsBitmap& bitmap, int x, int y)
 {