(perl #133981) fix for Win32 setlocale() abort

This appears to abort because the supplied locale string isn't validly
encoded in the current code page, so we see the following steps:

1) an internal sizing call to mbstowcs_s() fails, but

2) the calling (CRT) code doesn't handle that, allocating a zero length
buffer

3) mbstowcs_s() is called with a buffer and a zero size, causing the
exception.

Since it's the conversion that fails, perform our own conversion.

Rather than using the current code page always use CP_UTF8, since
this is perl's typical non-Latin1 encoding.

Unfortunately we don't have the SVf_UTF8 flag at this point, so
all we can do is assume UTF-8.

This introduces a change in behaviour - previously locale names
were interpreted in the current code page, but most locale names
are ASCII, so it shouldn't matter.

One issue is that the return value is freed on the next LEAVE, but
all callers immediately use or copy the string.

locale.c

@@ -2084,6 +2084,57 @@ S_new_collate(pTHX_ const char *newcoll)
 
 #ifdef WIN32
 
+#define USE_WSETLOCALE
+
+#ifdef USE_WSETLOCALE
+
+STATIC char *
+S_wrap_wsetlocale(pTHX_ int category, const char *locale) {
+    wchar_t *wlocale;
+    wchar_t *wresult;
+    char *result;
+
+    if (locale) {
+        int req_size =
+            MultiByteToWideChar(CP_UTF8, 0, locale, -1, NULL, 0);
+
+        if (!req_size) {
+            errno = EINVAL;
+            return NULL;
+        }
+
+        Newx(wlocale, req_size, wchar_t);
+        if (!MultiByteToWideChar(CP_UTF8, 0, locale, -1, wlocale, req_size)) {
+            Safefree(wlocale);
+            errno = EINVAL;
+            return NULL;
+        }
+    }
+    else {
+        wlocale = NULL;
+    }
+    wresult = _wsetlocale(category, wlocale);
+    Safefree(wlocale);
+    if (wresult) {
+        int req_size =
+            WideCharToMultiByte(CP_UTF8, 0, wresult, -1, NULL, 0, NULL, NULL);
+        Newx(result, req_size, char);
+        SAVEFREEPV(result); /* is there something better we can do here? */
+        if (!WideCharToMultiByte(CP_UTF8, 0, wresult, -1,
+                                 result, req_size, NULL, NULL)) {
+            errno = EINVAL;
+            return NULL;
+        }
+    }
+    else {
+        result = NULL;
+    }
+
+    return result;
+}
+
+#endif
+
 STATIC char *
 S_win32_setlocale(pTHX_ int category, const char* locale)
 {
@@ -2141,7 +2192,11 @@ S_win32_setlocale(pTHX_ int category, const char* locale)
 
     }
 
+#ifdef USE_WSETLOCALE
+    result = S_wrap_wsetlocale(aTHX_ category, locale);
+#else
     result = setlocale(category, locale);
+#endif
     DEBUG_L(STMT_START {
                 dSAVE_ERRNO;
                 PerlIO_printf(Perl_debug_log, "%s:%d: %s\n", __FILE__, __LINE__,
@@ -2162,7 +2217,11 @@ S_win32_setlocale(pTHX_ int category, const char* locale)
     for (i = 0; i < LC_ALL_INDEX; i++) {
         result = PerlEnv_getenv(category_names[i]);
         if (result && strNE(result, "")) {
-            setlocale(categories[i], result);
+#ifdef USE_WSETLOCALE
+            S_wrap_wsetlocale(aTHX_ categories[i], locale);
+#else
+            setlocale(categories[i], locale);
+#endif
             DEBUG_Lv(PerlIO_printf(Perl_debug_log, "%s:%d: %s\n",
                 __FILE__, __LINE__,
                 setlocale_debug_string(categories[i], result, "not captured")));