locale.c: Add a fcn to display LC_ALL

This is trivial on a platform that has LC_ALL, but requires extra work
on platforms that don't.

embed.fnc

@@ -3233,6 +3233,7 @@ SG   |bool   |sv_derived_from_svpvn  |NULLOK SV *sv			\
 #if defined(PERL_IN_LOCALE_C)
 #  ifdef USE_LOCALE
 ST	|unsigned int|get_category_index|const int category|NULLOK const char * locale
+S	|const char *|get_LC_ALL_display
 S	|unsigned|get_locale_string_utf8ness_i				\
 				|NULLOK const char * locale		\
 				|const unsigned cat_index		\

embed.h

@@ -1740,6 +1740,7 @@
 #  endif
 #  if defined(PERL_IN_LOCALE_C)
 #    if defined(USE_LOCALE)
+#define get_LC_ALL_display()	S_get_LC_ALL_display(aTHX)
 #define get_category_index	S_get_category_index
 #define get_locale_string_utf8ness_i(a,b,c,d)	S_get_locale_string_utf8ness_i(aTHX_ a,b,c,d)
 #define is_codeset_name_UTF8	S_is_codeset_name_UTF8

locale.c

@@ -1612,6 +1612,36 @@ S_calculate_LC_ALL(pTHX_ const char ** individ_locales)
     return aggregate_locale;
 }
 
+STATIC const char *
+S_get_LC_ALL_display(pTHX)
+{
+
+#  ifdef LC_ALL
+
+    return querylocale_c(LC_ALL);
+
+#  else
+
+    unsigned int i;
+    const char * retval;
+    const char * curlocales[NOMINAL_LC_ALL_INDEX];
+
+    for (i = 0; i < NOMINAL_LC_ALL_INDEX; i++) {
+        curlocales[i] = savepv(querylocale_i(i));
+    }
+
+    retval = calculate_LC_ALL(curlocales);
+
+    for (i = 0; i < NOMINAL_LC_ALL_INDEX; i++) {
+        Safefree(curlocales[i]);
+    }
+
+    return retval;
+
+#  endif
+
+}
+
 STATIC void
 S_setlocale_failure_panic_i(pTHX_
                             const unsigned int cat_index,

proto.h

@@ -5184,6 +5184,8 @@ PERL_CALLCONV SV*	Perl_hfree_next_entry(pTHX_ HV *hv, STRLEN *indexp);
 #endif
 #if defined(PERL_IN_LOCALE_C)
 #  if defined(USE_LOCALE)
+STATIC const char *	S_get_LC_ALL_display(pTHX);
+#define PERL_ARGS_ASSERT_GET_LC_ALL_DISPLAY
 STATIC unsigned int	S_get_category_index(const int category, const char * locale);
 #define PERL_ARGS_ASSERT_GET_CATEGORY_INDEX
 STATIC unsigned	S_get_locale_string_utf8ness_i(pTHX_ const char * locale, const unsigned cat_index, const char * string, const int known_utf8);