Building the current sources from git on Solaris gets a warning of:
"xcb_conn.c", line 43: warning: implicit function declaration: fcntl

This is because xcb_conn.c includes <sys/fcntl.h> instead of the POSIX-standard
<fcntl.h> - the fix is simply:

--- a/xcb/src/xcb_conn.c
+++ b/xcb/src/xcb_conn.c
@@ -32,7 +32,7 @@
 #include <stdlib.h>
 #include <netinet/in.h>
 #include <sys/select.h>
-#include <sys/fcntl.h>
+#include <fcntl.h>
 #include <errno.h>

 #include "xcb.h"