OSX/scons: Try to get rid of buildproblems with openjpeg enabled in certain build environments and prepend SDK_FLAGS to CFLAGS always

extern/libopenjpeg/SConscript

@@ -13,6 +13,8 @@ defs = []
 if env['OURPLATFORM'] in ('win32-vc', 'win64-vc'):
     flags = []
     defs.append('OPJ_STATIC')
+elif env['OURPLATFORM'] == 'darwin':
+    flags = ['-Wall', '-O3', '-ffast-math', '-std=c99'] + env['CCFLAGS'] # to supply SDK_FLAGS here
 else:
     flags = ['-Wall', '-O3', '-ffast-math', '-std=c99']