Fix build Git for Windows in mingw32

diff --git a/compat/nedmalloc/malloc.c.h b/compat/nedmalloc/malloc.c.h
index b833ff9225..c7e0e757ed 100644
--- a/compat/nedmalloc/malloc.c.h
+++ b/compat/nedmalloc/malloc.c.h
@@ -502,6 +502,8 @@ MAX_RELEASE_CHECK_RATE   default: 4095 unless not HAVE_MMAP
 #ifndef _WIN32_WINNT
 #define _WIN32_WINNT 0x403
 #endif
+#undef  _WIN32_WINNT
+#define _WIN32_WINNT 0x0501
 #include <windows.h>
 #define HAVE_MMAP 1
 #define HAVE_MORECORE 0
diff --git a/compat/poll/poll.c b/compat/poll/poll.c
index b10adc780f..b182e25c52 100644
--- a/compat/poll/poll.c
+++ b/compat/poll/poll.c
@@ -42,6 +42,8 @@
 # if defined (_MSC_VER) && !defined(_WIN32_WINNT)
 #  define _WIN32_WINNT 0x0502
 # endif
+#undef  _WIN32_WINNT
+#define _WIN32_WINNT 0x0501
 # include <winsock2.h>
 # include <windows.h>
 # include <io.h>
diff --git a/git-compat-util.h b/git-compat-util.h
index c1e9bb0170..b215faff9d 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -149,6 +149,8 @@
 # if defined (_MSC_VER) && !defined(_WIN32_WINNT)
 #  define _WIN32_WINNT 0x0502
 # endif
+#undef  _WIN32_WINNT
+#define _WIN32_WINNT 0x0501
 #define WIN32_LEAN_AND_MEAN  /* stops windows.h including winsock.h */
 #include <winsock2.h>
 #include <windows.h>
diff --git a/http.c b/http.c
index cc6f7ca11b..9d1e76e7f1 100644
--- a/http.c
+++ b/http.c
@@ -1,3 +1,10 @@
+#ifdef __MINGW32__
+#include <io.h>
+#ifndef HAVE_FSEEKO
+#define ftello ftell
+#define fseeko fseek
+#endif
+#endif
 #include "git-compat-util.h"
 #include "http.h"
 #include "pack.h"