locale.c: Add static fcn to analyze locale codeset

It determines if the name indicates it is UTF-8 or not.  There are
several variant spellings in use, and this hides that from the the
callers.

It won't be actually used until the next commit

embed.fnc

@@ -3254,6 +3254,7 @@ Sr	|void	|setlocale_failure_panic_i|const unsigned int cat_index	\
 S	|void	|set_numeric_radix|const bool use_locale
 S	|void	|new_numeric	|NULLOK const char* newnum
 S	|void	|new_LC_ALL	|NULLOK const char* unused
+ST	|bool	|is_codeset_name_UTF8|NN const char * name
 #    ifdef USE_POSIX_2008_LOCALE
 S	|const char*|emulate_setlocale_i|const unsigned int index	\
 				    |NULLOK const char* new_locale	\

embed.h

@@ -1712,6 +1712,7 @@
 #    if defined(USE_LOCALE)
 #define category_name		S_category_name
 #define get_category_index	S_get_category_index
+#define is_codeset_name_UTF8	S_is_codeset_name_UTF8
 #define new_LC_ALL(a)		S_new_LC_ALL(aTHX_ a)
 #define new_collate(a)		S_new_collate(aTHX_ a)
 #define new_ctype(a)		S_new_ctype(aTHX_ a)

locale.c

@@ -5534,6 +5534,31 @@ Perl__is_cur_LC_category_utf8(pTHX_ int category)
     return is_utf8;
 }
 
+STATIC bool
+S_is_codeset_name_UTF8(const char * name)
+{
+    /* Return a boolean as to if the passed-in name indicates it is a UTF-8
+     * code set.  Several variants are possible */
+    const Size_t len = strlen(name);
+
+    PERL_ARGS_ASSERT_IS_CODESET_NAME_UTF8;
+
+#  ifdef WIN32
+
+    /* http://msdn.microsoft.com/en-us/library/windows/desktop/dd317756.aspx */
+    if (memENDs(name, len, "65001")) {
+        return TRUE;
+    }
+
+#  endif
+               /* 'UTF8' or 'UTF-8' */
+    return (    inRANGE(len, 4, 5)
+            &&  name[len-1] == '8'
+            && (   memBEGINs(name, len, "UTF")
+                || memBEGINs(name, len, "utf"))
+            && (len == 4 || name[3] == '-'));
+}
+
 #endif
 
 bool

proto.h

@@ -5133,6 +5133,9 @@ STATIC const char*	S_category_name(const int category);
 #define PERL_ARGS_ASSERT_CATEGORY_NAME
 STATIC unsigned int	S_get_category_index(const int category, const char * locale);
 #define PERL_ARGS_ASSERT_GET_CATEGORY_INDEX
+STATIC bool	S_is_codeset_name_UTF8(const char * name);
+#define PERL_ARGS_ASSERT_IS_CODESET_NAME_UTF8	\
+	assert(name)
 STATIC void	S_new_LC_ALL(pTHX_ const char* unused);
 #define PERL_ARGS_ASSERT_NEW_LC_ALL
 STATIC void	S_new_collate(pTHX_ const char* newcoll);