package/libcap: don't overwrite 'empty' when generating loader.txt

package/libcap: don't overwrite 'empty' when generating loader.txt

Upstream commit [1] introduced an invocation of objcopy to generat
loader.txt. However, objcopy, if not provided with an output file, will
overwrite the input file. This is usually harmless because it will be
identical, but the timestamp is updated. This may cause 'empty' to be
newer than 'loader.txt', which causes 'loader.txt' and its dependencies
to be rebuilt during 'make install'

We provide a different set of parameters during 'make install'. In
particular, we no longer pass in HOST_CONFIGURE_OPTS, so we no longer
set LDFLAGS. Thus, there is no -Wl,rpath option that is passed in, which
causes the resulting binaries to have an incorrect RPATH.

Fix this by adding /dev/null as the output file in the objcopy
invocation.

Patch was sent upstream, but there's no mailing list, just a single
person.

Fixes: http://autobuild.buildroot.net/results/600/600aff5b839b48db80751cace5fa9670b7a3d698
(hopefully)

[1] https://git.kernel.org/pub/scm/libs/libcap/libcap.git/commit/?id=efd293947f940180eedd8d0915b124f4aedccc08

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>