fix stupid M_PI crap for MSVC

gfx/cairo/libpixman/src/fbcompose.c

@@ -36,6 +36,11 @@
 #ifdef _MSC_VER
 #define _USE_MATH_DEFINES
 #endif
+
+#ifndef M_PI
+#define M_PI 3.14159265358979323846
+#endif
+
 #include <math.h>
 
 // #define PIXMAN_CONVOLUTION