Special case localeconv when NUMERIC, MONETARY must be C

When both these categories are C, we don't need to call localeconv(),
which can be expensive because it may mean toggling locales.  Instead
the answers are well defined by the C Standard.  This adds a function
that returns those, and #ifdef's to locale.c to compile to use the
special function instead of the more general one if both categories must
be C.

A future commit will extend the use of this new function to more cases.

embed.fnc

@@ -4405,12 +4405,12 @@ Sf	|char * |strftime_tm	|NN const char *fmt			\
 				|NN const struct tm *mytm
 # if defined(HAS_LOCALECONV)
 S	|HV *	|my_localeconv	|const int item
-S	|void	|populate_hash_from_localeconv					\
-				|NN HV *hv					\
-				|NN const char *locale				\
-				|const PERL_UINT_FAST8_T which_mask		\
-				|NN const lconv_offset_t *strings[2]		\
-				|NULLOK const lconv_offset_t *integers[2]
+S	|void	|populate_hash_from_C_localeconv			\
+				|NN HV *hv				\
+				|NN const char *locale			\
+				|const PERL_UINT_FAST8_T which_mask	\
+				|NN const lconv_offset_t *strings[2]	\
+				|NN const lconv_offset_t *integers[2]
 # endif
 # if defined(USE_LOCALE)
 S	|const char *|calculate_LC_ALL_string					\
@@ -4521,6 +4521,14 @@ ST	|bool	|is_codeset_name_UTF8					\
 S	|void	|new_ctype	|NN const char *newctype		\
 				|bool force
 #   endif
+#   if defined(USE_LOCALE_MONETARY) || defined(USE_LOCALE_NUMERIC)
+S	|void	|populate_hash_from_localeconv				\
+				|NN HV *hv				\
+				|NN const char *locale			\
+				|const PERL_UINT_FAST8_T which_mask	\
+				|NN const lconv_offset_t *strings[2]	\
+				|NN const lconv_offset_t *integers[2]
+#   endif
 #   if defined(USE_LOCALE_NUMERIC)
 S	|void	|new_numeric	|NN const char *newnum			\
 				|bool force

embed.h

@@ -1303,7 +1303,7 @@
 #     define strftime_tm(a,b)                   S_strftime_tm(aTHX_ a,b)
 #     if defined(HAS_LOCALECONV)
 #       define my_localeconv(a)                 S_my_localeconv(aTHX_ a)
-#       define populate_hash_from_localeconv(a,b,c,d,e) S_populate_hash_from_localeconv(aTHX_ a,b,c,d,e)
+#       define populate_hash_from_C_localeconv(a,b,c,d,e) S_populate_hash_from_C_localeconv(aTHX_ a,b,c,d,e)
 #     endif
 #     if defined(USE_LOCALE)
 #       define calculate_LC_ALL_string(a,b,c,d) S_calculate_LC_ALL_string(aTHX_ a,b,c,d)
@@ -1343,6 +1343,9 @@
 #         define is_codeset_name_UTF8           S_is_codeset_name_UTF8
 #         define new_ctype(a,b)                 S_new_ctype(aTHX_ a,b)
 #       endif
+#       if defined(USE_LOCALE_MONETARY) || defined(USE_LOCALE_NUMERIC)
+#         define populate_hash_from_localeconv(a,b,c,d,e) S_populate_hash_from_localeconv(aTHX_ a,b,c,d,e)
+#       endif
 #       if defined(USE_LOCALE_NUMERIC)
 #         define new_numeric(a,b)               S_new_numeric(aTHX_ a,b)
 #       endif