use const-correct types with strchr, strstr, etc.

Because ccan/config.h #defines _GNU_SOURCE, glibc declares qualifier-
preserving generic prototypes for the twelve "qualifier-losing search
functions" (bsearch, bsearch_s, memchr, strchr, strpbrk, strrchr, strstr,
wcschr, wcspbrk, wcsrchr, wcsstr, wmemchr), even in -std=gnu11 mode.

Several places throughout the code base were calling these search functions
and inadvertently stripping away the constness of their return values,
triggering compilation errors due to -Werror. Fix up these call sites so
that the assignments of their return values do not implicitly discard the
const qualifier.

Changelog-None

Author: whitslack

common/wireaddr.c

@@ -292,10 +292,10 @@ char *fmt_wireaddr(const tal_t *ctx, const struct wireaddr *a)
 bool separate_address_and_port(const tal_t *ctx, const char *arg,
 			       char **addr, u16 *port)
 {
-	char *portcolon;
+	const char *portcolon;
 
 	if (strstarts(arg, "[")) {
-		char *end = strchr(arg, ']');
+		const char *end = strchr(arg, ']');
 		if (!end)
 			return false;
 		/* Copy inside [] */

connectd/tor_autoservice.c

@@ -200,7 +200,7 @@ static void negotiate_auth(struct rbuf *rbuf, const char *tor_password)
 	tor_send_cmd(rbuf, "PROTOCOLINFO 1");
 
 	while ((line = tor_response_line(rbuf)) != NULL) {
-		const char *p;
+		char *p;
 
 		if (!strstarts(line, "AUTH METHODS="))
 			continue;

db/db_sqlite3.c

@@ -438,8 +438,8 @@ static char **prepare_table_manip(const tal_t *ctx,
 				  struct db *db, const char *tablename)
 {
 	sqlite3_stmt *stmt;
-	const char *sql;
-	char *cmd, *bracket;
+	const char *sql, *bracket;
+	char *cmd;
 	char **parts;
 	int err;
 	struct db_sqlite3 *wrapper = (struct db_sqlite3 *)db->conn;

plugins/fetchinvoice.c

@@ -1029,7 +1029,7 @@ struct command_result *json_fetchinvoice(struct command *cmd,
 	 *       - `domain` set to the post-@ part of the BIP 353 HRN.
 	 */
 	if (bip353) {
-		char *at;
+		const char *at;
 		if (!utf8_check(bip353, strlen(bip353)))
 			return command_fail(cmd, JSONRPC2_INVALID_PARAMS,
 					    "invalid UTF-8 for bip353");

plugins/spender/multifundchannel.c

@@ -1845,7 +1845,7 @@ param_destinations_array(struct command *cmd, const char *name,
 	json_for_each_arr(i, json_dest, tok) {
 		struct multifundchannel_destination *dest;
 		const char *id;
-		char *addrhint;
+		const char *addrhint;
 		struct amount_sat *amount, *request_amt;
 		bool *announce;
 		struct amount_msat *push_msat;

tools/check-bolt.c

@@ -236,7 +236,7 @@ static void fail_mismatch(const char *filename,
 static bool find_strings(const char *bolttext, char **strings, size_t nstrings)
 {
 	const char *p = bolttext;
-	char *find;
+	const char *find;
 
 	if (nstrings == 0)
 		return true;