This patch reverts the following:

jason-tishler · jason-tishler · commit 9181c94e0525 · 2003-02-05T15:16:17.000Z
It also prevents building against the real X headers, if installed.

After discussions with the Cygwin project lead, I believe that building
against the real X headers is OK. Especially, since the psuedo-X headers
are *not* installed by the Cygwin Tcl/Tk binary package.
diff --git a/setup.py b/setup.py
@@ -953,11 +953,6 @@ def detect_tkinter(self, inc_dirs, lib_dirs):
         if platform == 'sunos5':
             include_dirs.append('/usr/openwin/include')
             added_lib_dirs.append('/usr/openwin/lib')
-        elif platform == 'cygwin':
-            # Verify that the pseudo-X headers are installed before proceeding
-            x11_inc = find_file('X11/Xlib.h', [], inc_dirs)
-            if x11_inc is None:
-                return
         elif os.path.exists('/usr/X11R6/include'):
             include_dirs.append('/usr/X11R6/include')
             added_lib_dirs.append('/usr/X11R6/lib')
@@ -969,6 +964,12 @@ def detect_tkinter(self, inc_dirs, lib_dirs):
             include_dirs.append('/usr/X11/include')
             added_lib_dirs.append('/usr/X11/lib')
 
+        # If Cygwin, then verify that X is installed before proceeding
+        if platform == 'cygwin':
+            x11_inc = find_file('X11/Xlib.h', [], include_dirs)
+            if x11_inc is None:
+                return
+
         # Check for BLT extension
         if self.compiler.find_library_file(lib_dirs + added_lib_dirs,
                                            'BLT8.0'):
