cairo: pass --disable-xlib to config if no x11

It appears that cairo's configure script, at least on MacOS but perhaps
elsewhere, unconditionally enables xlib support, even if the library
isn't present, which breaks the build on MacOS always (since x11 is
disabled by default now). This explicitly passes `--disable-x11` if
x11Support is set to false, which fixes the build for me.

pkgs/development/libraries/cairo/default.nix

@@ -61,7 +61,7 @@ in stdenv.mkDerivation rec {
     ++ optional glSupport libGL
     ; # TODO: maybe liblzo but what would it be for here?
 
-  configureFlags = if stdenv.isDarwin then [
+  configureFlags = (if stdenv.isDarwin then [
     "--disable-dependency-tracking"
     "--enable-quartz"
     "--enable-quartz-font"
@@ -71,7 +71,7 @@ in stdenv.mkDerivation rec {
     ++ optional xcbSupport "--enable-xcb"
     ++ optional glSupport "--enable-gl"
     ++ optional pdfSupport "--enable-pdf"
-  );
+  )) ++ optional (!x11Support) "--disable-xlib";
 
   preConfigure =
   # On FreeBSD, `-ldl' doesn't exist.