locale.c: Split up S_setlocale_from_aggregate_LC_ALL

This splits out the parsing of the LC_ALL string from the locale
setting.  Future commits will use the parse portion in more places.

The new code doesn't panic on syntax errors, unlike the old.  This is
because we should never panic on user input, but return failure instead.

embed.fnc

@@ -4424,13 +4424,21 @@ S	|const char *|setlocale_from_aggregate_LC_ALL			\
 				|NN const char *locale			\
 				|const line_t line
 S	|locale_t|use_curlocale_scratch
+#     if defined(LC_ALL)
+S	|parse_LC_ALL_string_return|parse_LC_ALL_string 		\
+				|NN const char *string			\
+				|NN const char **output 		\
+				|const line_t caller_line
+#     endif
 #     if !defined(USE_QUERYLOCALE)
 S	|void	|update_PL_curlocales_i 				\
 				|const unsigned int index		\
 				|NN const char *new_locale
 #     endif
-#   elif  defined(USE_LOCALE_THREADS) && !defined(USE_THREAD_SAFE_LOCALE) && \
-         !defined(USE_THREAD_SAFE_LOCALE_EMULATION)
+#   elif  defined(USE_LOCALE_THREADS) &&                  \
+         !defined(USE_THREAD_SAFE_LOCALE) &&              \
+         !defined(USE_THREAD_SAFE_LOCALE_EMULATION) /* &&
+         !defined(USE_POSIX_2008_LOCALE) */
 S	|bool	|less_dicey_bool_setlocale_r				\
 				|const int cat				\
 				|NN const char *locale

embed.h

@@ -1304,12 +1304,16 @@
 #         define querylocale_2008_i(a)          S_querylocale_2008_i(aTHX_ a)
 #         define setlocale_from_aggregate_LC_ALL(a,b) S_setlocale_from_aggregate_LC_ALL(aTHX_ a,b)
 #         define use_curlocale_scratch()        S_use_curlocale_scratch(aTHX)
+#         if defined(LC_ALL)
+#           define parse_LC_ALL_string(a,b,c)   S_parse_LC_ALL_string(aTHX_ a,b,c)
+#         endif
 #         if !defined(USE_QUERYLOCALE)
 #           define update_PL_curlocales_i(a,b)  S_update_PL_curlocales_i(aTHX_ a,b)
 #         endif
-#       elif  defined(USE_LOCALE_THREADS) &&     \
-             !defined(USE_THREAD_SAFE_LOCALE) && \
-             !defined(USE_THREAD_SAFE_LOCALE_EMULATION)
+#       elif  defined(USE_LOCALE_THREADS) &&                  \
+             !defined(USE_THREAD_SAFE_LOCALE) &&              \
+             !defined(USE_THREAD_SAFE_LOCALE_EMULATION) /* &&
+             !defined(USE_POSIX_2008_LOCALE) */
 #         define less_dicey_bool_setlocale_r(a,b) S_less_dicey_bool_setlocale_r(aTHX_ a,b)
 #         define less_dicey_setlocale_r(a,b)    S_less_dicey_setlocale_r(aTHX_ a,b)
 #       endif