win32: share code to find root prefix of path

Move unc_root_len() from ash to mingw32.c and use it in the new
function root_len(), which can be used in make_directory().

This reduces changes to upstream code and saves a few bytes.

1 files changed, 3 insertions, 0 deletions

diff --git a/include/mingw.h b/include/mingw.h
index 36c2f6805..7c9423cad 100644
--- a/include/mingw.h
+++ b/include/mingw.h
@@ -522,3 +522,6 @@ ULONGLONG CompatGetTickCount64(void);
 ssize_t get_random_bytes(void *buf, ssize_t count);
 int enumerate_links(const char *file, char *name);
 void hide_console(void);
+
+int unc_root_len(const char *dir);
+int root_len(const char *path);