Commit f4d9d7a removed support for version specific patches; but it also
broke applying of patches in the patches glibc dir.
Fix the issue by setting PATCH_DIR to $(PATH_PREFIX)/patches similar as
musl/common.mk.
Signed-off-by: Xinxing Hu <xinxing.huchn@gmail.com>
Signed-off-by: Hans Dedecker <dedeckeh@gmail.com>