build-sys: expand paths at make time

build-sys: expand paths at make time

autoconf docs about *dir variables (e.g bindir):

 ... A corollary is that you should not use these variables except in
 makefiles...

 ...you should not rely on AC_CONFIG_FILES to replace bindir and friends
 in your shell scripts and other files; instead, let make manage their
 replacement.

Signed-off-by: Karel Zak <kzak@redhat.com>