Visual Studio doesn't have unistd.h, and mysql2 compiles just fine.

lowjoel · lowjoel · commit c9a2bdd993ef · 2014-07-12T09:34:11.000+08:00
diff --git a/ext/mysql2/infile.c b/ext/mysql2/infile.c
@@ -1,7 +1,9 @@
 #include <mysql2_ext.h>
 
 #include <errno.h>
+#ifndef _MSC_VER
 #include <unistd.h>
+#endif
 #include <fcntl.h>
 
 #define ERROR_LEN 1024
