Run semantic analysis pass one if file doesn't exsit (#21379)

Noticed this while working on the other fixes from
#21331. If file doesn't exist, it
will be parsed with the old parser, even if the native parser is
enabled, so we need to run semantic analysis pass one on it.

Not adding a test because this will not be needed soon (and I am lazy,
sorry).

Author: ilevkivskyi

mypy/build.py

@@ -3314,7 +3314,9 @@ def semantic_analysis_pass1(self) -> None:
         #
         # TODO: This should not be considered as a semantic analysis
         #     pass -- it's an independent pass.
-        if not options.native_parser:
+        if not options.native_parser or not self.manager.fscache.exists(
+            self.xpath, real_only=True
+        ):
             analyzer = SemanticAnalyzerPreAnalysis()
             with self.wrap_context():
                 analyzer.visit_file(self.tree, self.xpath, self.id, options)