Clarify and simplify a bit as we don't have any X11 option on Mac OS X anyway

configure.in

@@ -2714,6 +2714,7 @@ cygwin*)
 darwin*)
     COM=GCC
     GUI=UNX
+    # Not sure if "Aqua" is the right term to use?
     GUIBASE="aqua"
     OS=MACOSX
     P_SEP=:
@@ -7246,30 +7247,7 @@ AC_SUBST(SYSTEM_SAMPLEICC)
 AC_SUBST(SAMPLEICC_LIBS)
 AC_SUBST(SAMPLEICC_CFLAGS)
 
-dnl ===================================================================
-dnl Checks for libraries.
-dnl ===================================================================
-dnl Check for Mac OS X native GUI, which may is now required; the X11 build is no longer supported
-dnl See if we have the AppKit framework for building with Quartz graphics.
-
-if test  "$_os" = "Darwin"; then
-    if test "x$with_x" = "xyes"; then
-        AC_MSG_ERROR([X11 build is no longer supported on MacOSX, please use the native aqua build])
-    else
-        AC_MSG_CHECKING([for /System/Library/Frameworks/AppKit.framework])
-        if test -d "/System/Library/Frameworks/AppKit.framework/"; then
-            AC_MSG_RESULT([yes])
-            x_includes="no_x_includes"
-            x_libraries="no_x_libraries"
-            dnl disable some things used on other Unix versions but not on the aqua build
-            enable_gtk=no
-        else
-            AC_MSG_ERROR([No AppKit.framewrok found])
-        fi
-    fi
-fi
-
-if test $_os = iOS -o $_os = Android; then
+if test $_os = Darwin -o $_os = iOS -o $_os = Android; then
     enable_gtk=no
 fi
 
@@ -7293,10 +7271,7 @@ AC_SUBST(ENABLE_NSPLUGIN)
 dnl ***************************************
 dnl testing for X libraries and includes...
 dnl ***************************************
-if test "$_os" = "Darwin" -a "x$x_includes" = "xno_x_includes"; then
-    dnl Mac OS X using Aqua graphics. Don't check for X11.
-    :
-elif test "$_os" != "WINNT" -a "$_os" != "Android" -a "$_os" != "iOS"; then
+if test $_os != Darwin -a $_os != WINNT -a $_os != Android -a $_os != iOS; then
     AC_PATH_X
     AC_PATH_XTRA
     CPPFLAGS="$CPPFLAGS $X_CFLAGS"