depends: use "mkdir -p" when installing xproto

It looks like the mkdir detection in xproto is broken on Alpine. Ensure
we always use `mkdir -p`.

Fixes bitcoin#32494.

Author: fanquake

depends/packages/xproto.mk

@@ -21,6 +21,8 @@ define $(package)_build_cmds
   $(MAKE)
 endef
 
+# mkdir detection is broken on Alpine. Set MKDIRPROG to ensure we always
+# use "mkdir -p", and avoid parallelism issues during install.
 define $(package)_stage_cmds
-  $(MAKE) DESTDIR=$($(package)_staging_dir) install
+  $(MAKE) MKDIRPROG="mkdir -p" DESTDIR=$($(package)_staging_dir) install
 endef