package/apr: Bump version to 1.5.1

apr-0001-cross-compile.patch: Fix cross compilation
Fix top_builddir in usr/build-1/apr_rules.mk

[Thomas: rename apr-0001-cross-compile.patch to
0001-cross-compile.patch.]

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>