hash.c, symbol.c, string.c, mruby-string-ext: undef lesser macro

Add #undef lesser after last usage to prevent macro redefinition
warnings when files are amalgamated into a single translation unit.

Co-authored-by: Claude <noreply@anthropic.com>

mrbgems/mruby-string-ext/src/string.c

@@ -1226,6 +1226,7 @@ str_casecmp(mrb_state *mrb, mrb_value self)
   if (len1 > len2)  return mrb_fixnum_value(1);
   return mrb_fixnum_value(-1);
 }
+#undef lesser
 
 /*
  * call-seq:

src/hash.c

@@ -2281,3 +2281,4 @@ mrb_init_hash(mrb_state *mrb)
   mrb_define_method_id(mrb, h, MRB_SYM(__merge),         mrb_hash_merge_m,     MRB_ARGS_REQ(1));
   mrb_define_method_id(mrb, h, MRB_SYM(__compact),       mrb_hash_compact,     MRB_ARGS_NONE()); /* implementation of Hash#compact! */
 }
+#undef lesser

src/string.c

@@ -1257,6 +1257,7 @@ mrb_str_cmp(mrb_state *mrb, mrb_value str1, mrb_value str2)
   if (retval > 0) return 1;
   return -1;
 }
+#undef lesser
 
 /* 15.2.10.5.3  */
 

src/symbol.c

@@ -977,6 +977,7 @@ sym_cmp(mrb_state *mrb, mrb_value s1)
     return mrb_fixnum_value(-1);
   }
 }
+#undef lesser
 
 void
 mrb_init_symbol(mrb_state *mrb)