fix mbstring.c -Wsingle-bit-bitfield-constant-conversion

This opts to fix it in the same way as GH-11729 did, by converting
it to a boolean.

Author: morrisonlevi

ext/mbstring/mbstring.c

@@ -4203,9 +4203,9 @@ PHP_FUNCTION(mb_send_mail)
 	char *to_r = NULL;
 	char *force_extra_parameters = INI_STR("mail.force_extra_parameters");
 	struct {
-		int cnt_type:1;
-		int cnt_trans_enc:1;
-	} suppressed_hdrs = { 0, 0 };
+		bool cnt_type:1;
+		bool cnt_trans_enc:1;
+	} suppressed_hdrs = { false, false };
 
 	char *p;
 	enum mbfl_no_encoding;
@@ -4288,7 +4288,7 @@ PHP_FUNCTION(mb_send_mail)
 				}
 			}
 		}
-		suppressed_hdrs.cnt_type = 1;
+		suppressed_hdrs.cnt_type = true;
 	}
 
 	if ((s = zend_hash_str_find(&ht_headers, "content-transfer-encoding", sizeof("content-transfer-encoding") - 1))) {
@@ -4308,7 +4308,7 @@ PHP_FUNCTION(mb_send_mail)
 				body_enc =	&mbfl_encoding_8bit;
 				break;
 		}
-		suppressed_hdrs.cnt_trans_enc = 1;
+		suppressed_hdrs.cnt_trans_enc = true;
 	}
 
 	/* To: */