bpo-34523: Fix C locale coercion on FreeBSD CURRENT (GH-10672)

bpo-34523, bpo-35290: C locale coercion now resets the Python
internal "force ASCII" mode. This change fix the filesystem encoding
on FreeBSD CURRENT, which has a new "C.UTF-8" locale, when
the UTF-8 mode is disabled.

Add _Py_ResetForceASCII(): _Py_SetLocaleFromEnv() now calls it.
diff --git a/Python/pylifecycle.c b/Python/pylifecycle.c
index af3d5ef..6de32de 100644
--- a/Python/pylifecycle.c
+++ b/Python/pylifecycle.c
@@ -5,6 +5,7 @@
 #include "Python-ast.h"
 #undef Yield   /* undefine macro conflicting with <winbase.h> */
 #include "pycore_context.h"
+#include "pycore_fileutils.h"
 #include "pycore_hamt.h"
 #include "pycore_pathconfig.h"
 #include "pycore_pylifecycle.h"
@@ -394,6 +395,7 @@
 char *
 _Py_SetLocaleFromEnv(int category)
 {
+    char *res;
 #ifdef __ANDROID__
     const char *locale;
     const char **pvar;
@@ -440,10 +442,12 @@
         }
     }
 #endif
-    return setlocale(category, utf8_locale);
-#else /* __ANDROID__ */
-    return setlocale(category, "");
-#endif /* __ANDROID__ */
+    res = setlocale(category, utf8_locale);
+#else /* !defined(__ANDROID__) */
+    res = setlocale(category, "");
+#endif
+    _Py_ResetForceASCII();
+    return res;
 }