Stop dangling symlinks in the include dir from breaking the build.
https://github.com/python/cpython/pull/113466

diff --git a/setup.py b/setup.py
index 4f122b62e0e708..ad8fb81b218ebd 100644
--- setup.py
+++ setup.py
@@ -224,6 +224,7 @@ def is_macosx_sdk_path(path):
 
 def grep_headers_for(function, headers):
     for header in headers:
+        if not os.path.exists(header): continue
         with open(header, 'r', errors='surrogateescape') as f:
             if function in f.read():
                 return True