patch libgit2 so 0.21.3 can compile with mingw

deps/Makefile

@@ -1788,6 +1788,7 @@ ifeq ($(BUILD_OS),WINNT)
 else
 	$(TAR) zxf $<
 endif
+	cd libgit2-$(LIBGIT2_VER) && patch -p1 < ../libgit2-0.21.3-mingw.patch
 	touch -c $@
 libgit2-$(LIBGIT2_VER)/build/Makefile: libgit2-$(LIBGIT2_VER)/CMakeLists.txt
 	mkdir -p libgit2-$(LIBGIT2_VER)/build

deps/libgit2-0.21.3-mingw.patch

@@ -0,0 +1,25 @@
+diff --git a/src/path.h b/src/path.h
+index 6c50334..444337b 100644
+--- a/src/path.h
++++ b/src/path.h
+@@ -8,6 +8,7 @@
+ #define INCLUDE_path_h__
+
+ #include "common.h"
++#include "posix.h"
+ #include "buffer.h"
+ #include "vector.h"
+
+diff --git a/src/win32/path_w32.h b/src/win32/path_w32.h
+index 1d10166..033afbb 100644
+--- a/src/win32/path_w32.h
++++ b/src/win32/path_w32.h
+@@ -7,6 +7,8 @@
+ #ifndef INCLUDE_git_path_w32_h__
+ #define INCLUDE_git_path_w32_h__
+
++#include "common.h"
++
+ /*
+  * Provides a large enough buffer to support Windows paths:  MAX_PATH is
+  * 260, corresponding to a maximum path length of 259 characters plus a