[PATCH libaio 02/16] build: Fix DESTDIR and pathname variables handling

[PATCH libaio 02/16] build: Fix DESTDIR and pathname variables handling

The convention for DESTDIR is that it is only prefixed during the
install target. In this case we postpone that to the inner Makefile
so that it can be invoked directly while preserving the expected
semantics. We should also prefer the user specified pathname variables
if already set in any way, and do not need to pass them explicitly
to the sub-make.

Signed-off-by: Guillem Jover <guillem@hadrons.org>
Gbp-Pq: Name 0002-build-Fix-DESTDIR-and-pathname-variables-handling.patch