bpo-38835: Exclude PyFPE macros from the stable API (GH-17228)

Exclude PyFPE_START_PROTECT() and PyFPE_END_PROTECT() macros of
pyfpe.h from Py_LIMITED_API (stable API).
diff --git a/Include/pyfpe.h b/Include/pyfpe.h
index 5a99e39..cc2def6 100644
--- a/Include/pyfpe.h
+++ b/Include/pyfpe.h
@@ -1,5 +1,7 @@
 #ifndef Py_PYFPE_H
 #define Py_PYFPE_H
+/* Header excluded from the stable API */
+#ifndef Py_LIMITED_API
 
 /* These macros used to do something when Python was built with --with-fpectl,
  * but support for that was dropped in 3.7. We continue to define them though,
@@ -9,4 +11,5 @@
 #define PyFPE_START_PROTECT(err_string, leave_stmt)
 #define PyFPE_END_PROTECT(v)
 
+#endif /* !defined(Py_LIMITED_API) */
 #endif /* !Py_PYFPE_H */