Assert that include directory exists in Ports.install_headers. NFC (#17495)

This is an attempt to help debug #17060.

Author: sbc100

tools/ports/__init__.py

@@ -85,6 +85,7 @@ def install_header_dir(src_dir, target=None):
   def install_headers(src_dir, pattern='*.h', target=None):
     logger.debug('install_headers')
     dest = Ports.get_include_dir()
+    assert os.path.exists(dest)
     if target:
       dest = os.path.join(dest, target)
       shared.safe_ensure_dirs(dest)