Fix duplicate basenames to support older VS

With Visual Studio versions 2008 and older they ignore the full path to files and only check
the basename of the file to find a collision. Additionally, having duplicate basenames can break
other build tools like GYP.

This fixes https://github.com/libgit2/libgit2/issues/3356

src/path.c

@@ -10,7 +10,7 @@
 #include "repository.h"
 #ifdef GIT_WIN32
 #include "win32/posix.h"
-#include "win32/buffer.h"
+#include "win32/w32_buffer.h"
 #include "win32/w32_util.h"
 #include "win32/version.h"
 #else

src/win32/buffer.c → src/win32/w32_buffer.c

@@ -6,7 +6,7 @@
  */
 
 #include "common.h"
-#include "buffer.h"
+#include "w32_buffer.h"
 #include "../buffer.h"
 #include "utf-conv.h"
 
@@ -52,4 +52,3 @@ int git_buf_put_w(git_buf *buf, const wchar_t *string_w, size_t len_w)
 	buf->ptr[buf->size] = '\0';
 	return 0;
 }
-