Enable more warnings and fix few sign-related situations

Makefile

-CFLAGS=-Wall -O3 -std=gnu99 -ggdb3
+CFLAGS=-Wall -Wextra -Wno-unused -O3 -std=gnu99 -ggdb3
 
 all: compctld compctl
 

compctl.c

@@ -54,7 +54,7 @@ daemon_chat(char *cmd)
 		perror("sendmsg");
 		exit(EXIT_FAILURE);
 	}
-	if (sent < msg.msg_iov->iov_len) {
+	if ((size_t) sent < msg.msg_iov->iov_len) {
 		fprintf(stderr, "incomplete send %zd < %zu, FIXME\n", sent, msg.msg_iov->iov_len);
 		exit(EXIT_FAILURE);
 	}

compctld.c

@@ -47,8 +47,8 @@ memory_limits(size_t *minuser, size_t *mincomp, size_t *maxcomp, size_t *total)
 		*minuser = static_maxfree;
 
 	*mincomp = static_minfree;
-	*maxcomp = *total - *minuser;
-	if (*maxcomp < 0) *maxcomp = 0;
+	ssize_t smaxcomp = *total - *minuser;
+	*maxcomp = smaxcomp > 0 ? smaxcomp : 0;
 	/* maxcomp < mincomp may happen; they are used in different
 	 * settings. */
 }
@@ -101,7 +101,7 @@ mprintf(int fd, char *fmt, ...)
 		logperror("sendmsg");
 		return;
 	}
-	if (sent < iov.iov_len) {
+	if ((size_t) sent < iov.iov_len) {
 		syslog(LOG_INFO, "incomplete send %zd < %zu, FIXME", sent, iov.iov_len);
 		return;
 	}