Fix a few warnings that came up after turning on a dozen more warnings

gencode.c

@@ -1735,7 +1735,7 @@ gen_load_a(compiler_state_t *cstate, enum e_offrel offrel, u_int offset,
 
 	default:
 		abort();
-		return NULL;
+		/* NOTREACHED */
 	}
 	return s;
 }

rpcap-protocol.c

@@ -78,7 +78,7 @@
  * error message is returned in the 'errbuf' variable.
  */
 int
-rpcap_senderror(SOCKET sock, uint8 ver, unsigned short errcode, char *error, char *errbuf)
+rpcap_senderror(SOCKET sock, uint8 ver, unsigned short errcode, const char *error, char *errbuf)
 {
 	char sendbuf[RPCAP_NETBUF_SIZE];	/* temporary buffer in which data to be sent is buffered */
 	int sendbufidx = 0;			/* index which keeps the number of bytes currently buffered */

rpcap-protocol.h

@@ -445,6 +445,6 @@ struct rpcap_sampling
 
 extern void rpcap_createhdr(struct rpcap_header *header, uint8 ver, uint8 type, uint16 value, uint32 length);
 extern const char *rpcap_msg_type_string(uint8 type);
-extern int rpcap_senderror(SOCKET sock, uint8 ver, uint16 errcode, char *error, char *errbuf);
+extern int rpcap_senderror(SOCKET sock, uint8 ver, uint16 errcode, const char *error, char *errbuf);
 
 #endif

rpcapd/log-stderr.c

@@ -30,7 +30,7 @@ rpcapd_log(log_priority priority, const char *message, ...)
 
 	default:
 		abort();
-		return;
+		/* NOTREACHED */
 	}
 
 	fprintf(stderr, "rpcapd: %s", tag);

rpcapd/rpcapd.c

@@ -114,7 +114,7 @@ static unsigned __stdcall main_passive_serviceloop_thread(void *ptr);
 */
 static void printusage(void)
 {
-	char *usagetext =
+	const char *usagetext =
 	"USAGE:"
 	" "  PROGRAM_NAME " [-b <address>] [-p <port>] [-4] [-l <host_list>] [-a <host,port>]\n"
 	"              [-n] [-v] [-d] "

testprogs/selpolltest.c

@@ -70,7 +70,7 @@ main(int argc, char **argv)
 	bpf_u_int32 localnet, netmask;
 	register char *cp, *cmdbuf, *device;
 	int doselect, dopoll, dotimeout, dononblock;
-	char *mechanism;
+	const char *mechanism;
 	struct bpf_program fcode;
 	char ebuf[PCAP_ERRBUF_SIZE];
 	pcap_if_t *devlist;

testprogs/valgrindtest.c

@@ -233,7 +233,7 @@ main(int argc, char **argv)
 	int dorfmon, useactivate;
 	char ebuf[PCAP_ERRBUF_SIZE];
 	char *infile;
-	char *cmdbuf;
+	const char *cmdbuf;
 	pcap_if_t *devlist;
 	pcap_t *pd;
 	int status = 0;