Allow Perl to compile and work on Unicode releases without U+1E9E

U+1E9E LATIN CAPITAL LETTER SHARP S is handled specially by Perl,
because of its relationship to the infamous LATIN SMALL LETTER SHARP S,
which folds to 'ss', being the only character whose code point is < 256
to have a multi char fold, and this creates lots of special cases.

But U+1E9E wasn't in all Unicode releases.  Because Perl is supposed to
work with any release, we need to be able to compile when this character
isn't defined.  In some of those cases we use U+017F (LATIN SMALL LETTER
LONG S instead, which is in all releases.

4 files changed, 22 insertions, 8 deletions

diff --git a/regcomp.c b/regcomp.c
index fcaf153ef6..476ace0576 100644
--- a/regcomp.c
+++ b/regcomp.c
@@ -14014,9 +14014,15 @@ S_add_above_Latin1_folds(pTHX_ RExC_state_t *pRExC_state, const U8 cp, SV** invl
           *invlist = add_cp_to_invlist(*invlist,
                                         LATIN_CAPITAL_LETTER_Y_WITH_DIAERESIS);
             break;
+
+#ifdef LATIN_CAPITAL_LETTER_SHARP_S /* not defined in early Unicode releases */
+
         case LATIN_SMALL_LETTER_SHARP_S:
           *invlist = add_cp_to_invlist(*invlist, LATIN_CAPITAL_LETTER_SHARP_S);
             break;
+
+#endif
+
         default:
             /* Use deprecated warning to increase the chances of this being
              * output */
diff --git a/regexec.c b/regexec.c
index ec4ed861ab..0ea2aa070c 100644
--- a/regexec.c
+++ b/regexec.c
@@ -192,7 +192,7 @@ static const char* const non_utf8_target_but_utf8_required
                                         PL_utf8_swash_ptrs[_CC_WORDCHAR],     \
                                         "",                                   \
                                         PL_XPosix_ptrs[_CC_WORDCHAR],         \
-                                        LATIN_CAPITAL_LETTER_SHARP_S_UTF8);
+                                        LATIN_SMALL_LIGATURE_LONG_S_T_UTF8);
 
 #define PLACEHOLDER	/* Something for the preprocessor to grab onto */
 /* TODO: Combine JUMPABLE and HAS_TEXT to cache OP(rn) */
diff --git a/utf8.c b/utf8.c
index cbff7a7888..591174621e 100644
--- a/utf8.c
+++ b/utf8.c
@@ -2200,11 +2200,13 @@ Perl__to_utf8_fold_flags(pTHX_ const U8 *p, U8* ustrp, STRLEN *lenp, U8 flags)
 
 	if (flags & FOLD_FLAGS_LOCALE) {
 
-#           define CAP_SHARP_S   LATIN_CAPITAL_LETTER_SHARP_S_UTF8
 #           define LONG_S_T      LATIN_SMALL_LIGATURE_LONG_S_T_UTF8
+            const unsigned int long_s_t_len    = sizeof(LONG_S_T) - 1;
+
+#         ifdef LATIN_CAPITAL_LETTER_SHARP_S_UTF8
+#           define CAP_SHARP_S   LATIN_CAPITAL_LETTER_SHARP_S_UTF8
 
             const unsigned int cap_sharp_s_len = sizeof(CAP_SHARP_S) - 1;
-            const unsigned int long_s_t_len    = sizeof(LONG_S_T) - 1;
 
             /* Special case these two characters, as what normally gets
              * returned under locale doesn't work */
@@ -2217,7 +2219,9 @@ Perl__to_utf8_fold_flags(pTHX_ const U8 *p, U8* ustrp, STRLEN *lenp, U8 flags)
                               "resolved to \"\\x{17F}\\x{17F}\".");
                 goto return_long_s;
             }
-            else if (UTF8SKIP(p) == long_s_t_len
+            else
+#endif
+                 if (UTF8SKIP(p) == long_s_t_len
                      && memEQ((char *) p, LONG_S_T, long_s_t_len))
             {
                 /* diag_listed_as: Can't do %s("%s") on non-UTF-8 locale; resolved to "%s". */
@@ -2249,9 +2253,11 @@ Perl__to_utf8_fold_flags(pTHX_ const U8 *p, U8* ustrp, STRLEN *lenp, U8 flags)
 
                     /* But in these instances, there is an alternative we can
                      * return that is valid */
-                    if (original == LATIN_CAPITAL_LETTER_SHARP_S
-                        || original == LATIN_SMALL_LETTER_SHARP_S)
-                    {
+                    if (original == LATIN_SMALL_LETTER_SHARP_S
+#ifdef LATIN_CAPITAL_LETTER_SHARP_S /* not defined in early Unicode releases */
+                        || original == LATIN_CAPITAL_LETTER_SHARP_S
+#endif
+                    ) {
                         goto return_long_s;
                     }
                     else if (original == LATIN_SMALL_LIGATURE_LONG_S_T) {
diff --git a/utf8.h b/utf8.h
index 3e15707ff8..235d15c480 100644
--- a/utf8.h
+++ b/utf8.h
@@ -611,7 +611,9 @@ case any call to string overloading updates the internal UTF-8 encoding flag.
 #define GREEK_CAPITAL_LETTER_MU                 0x039C	/* Upper and title case
                                                            of MICRON */
 #define LATIN_CAPITAL_LETTER_Y_WITH_DIAERESIS   0x0178	/* Also is title case */
-#define LATIN_CAPITAL_LETTER_SHARP_S	        0x1E9E
+#ifdef LATIN_CAPITAL_LETTER_SHARP_S_UTF8
+#   define LATIN_CAPITAL_LETTER_SHARP_S	        0x1E9E
+#endif
 #define LATIN_SMALL_LETTER_LONG_S               0x017F
 #define LATIN_SMALL_LIGATURE_LONG_S_T           0xFB05
 #define LATIN_SMALL_LIGATURE_ST                 0xFB06