Get rid of unused defines in mingw.h (#583)

* Get rid of unused defines in mingw.h

src/mingw/mingw.h

@@ -5,15 +5,6 @@
 #define _USE_W32_SOCKETS 1
 #include <windows.h>
 
-#define ENOTCONN        WSAENOTCONN
-#define EWOULDBLOCK     WSAEWOULDBLOCK
-#define ENOBUFS         WSAENOBUFS
-#define ECONNRESET      WSAECONNRESET
-#define ESHUTDOWN       WSAESHUTDOWN
-#define EAFNOSUPPORT    WSAEAFNOSUPPORT
-#define EPROTONOSUPPORT WSAEPROTONOSUPPORT
-#define EINPROGRESS     WSAEINPROGRESS
-#define EISCONN         WSAEISCONN
 
 /* winsock doesn't feature poll(), so there is a version implemented
  * in terms of select() in mingw.c. The following definitions

src/mmap.c

@@ -19,15 +19,17 @@ void *mmap (void *addr, size_t len, int prot, int flags, int fd, long long  offs
 
     count = read(fd, buf, len);
 
-    if (count != len) {
+    if (count != (ssize_t)len) {
         free (buf);
         return MAP_FAILED;
     }
 
     return buf;
+    (void)flags;
 }
 
 int munmap (void *addr, size_t len) {
     free (addr);
     return 0;
+    (void)len;
 }