Allow to use FT_Library_SetLcdFilter in bundled FreeType.

For a default Qt build this change is a NOP, ftlcdfil.c is
ifdefed by FT_CONFIG_OPTION_SUBPIXEL_RENDERING, which we don't
define.

But for users who changed ftoption.h, or are using 3rdparty/freetype/devel/ftoption.h
instead of 3rdparty/freetype/include/freetype/config/ftoption.h they can now
enable Subpixel rendering without getting a build error.

Change-Id: I547e8a20514fcb97e4e56cb0100e9c2ed525f483
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@theqtcompany.com>
Reviewed-by: Konstantin Ritt <ritt.ks@gmail.com>