apr-util: Fix CFLAGS used in build

We need to use CFLAGS with the correct WORKDIR in them, replace those
in the sysroot file with the ones appropriate to the current recipe.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit 45edf189)
Signed-off-by: Steve Sakoman <steve@sakoman.com>