Fix libxcb/src compile with srcdir != builddir.
Fix libxcb/src compile with srcdir != builddir.

topcat/xcb-win32,OpenInkpot-archive/iplinux-libxcb,stapelberg/libxcb,OpenInkpot-archive/iplinux-libxcb,topcat/xcb-win32,topcat/xcb-win32,OpenInkpot-archive/iplinux-libxcb,stapelberg/libxcb,stapelberg/libxcb,topcat/xcb-win32,topcat/xcb-win32