Move sys/types.h include to posix.h for MinGW

posix.cc

@@ -33,7 +33,6 @@
 #include "posix.h"
 
 #include <limits.h>
-#include <sys/types.h>
 #include <sys/stat.h>
 
 #ifndef _WIN32

posix.h

@@ -29,6 +29,7 @@
 #define FMT_POSIX_H_
 
 #include <errno.h>
+#include <sys/types.h>  // required for fcntl.h on MinGW
 #include <fcntl.h>  // for O_RDONLY
 #include <stdio.h>