rb_enc_left_char_head(): take void*

Nobu doesn't like (char*) cast.

include/ruby/internal/encoding/encoding.h

@@ -694,7 +694,7 @@ rb_enc_prev_char(const char *s, const char *p, const char *e, const rb_encoding
  * @return     Pointer to the head of the character that contains `p`.
  */
 static inline char *
-rb_enc_left_char_head(const char *s, const char *p, const char *e, const rb_encoding *enc)
+rb_enc_left_char_head(const char *s, const void *p, const char *e, const rb_encoding *enc)
 {
     const OnigUChar *us = RBIMPL_CAST((const OnigUChar *)s);
     const OnigUChar *up = RBIMPL_CAST((const OnigUChar *)p);

string.c

@@ -5738,7 +5738,7 @@ rb_str_setbyte(VALUE str, VALUE index, VALUE value)
 		ENC_CODERANGE_SET(str, ENC_CODERANGE_VALID);
 	    goto end;
 	  case ENC_CODERANGE_VALID:
-            left = rb_enc_left_char_head(head, (char *)ptr, head+len, enc);
+	    left = rb_enc_left_char_head(head, ptr, head+len, enc);
 	    width = rb_enc_precise_mbclen(left, head+len, enc);
 	    *ptr = byte;
 	    nlen = rb_enc_precise_mbclen(left, head+len, enc);