package/jack2: backport two build fixes

0005-gcc7.patch fixes
http://autobuild.buildroot.net/results/c06/c0610325d7785dfa51c5d36775623ca8fa517f24/



0006-fix-ftbfs-with-clang.patch
fixes the subsequent build error:
common/memops.c.31.o: In function `sample_move_dither_rect_d16_sSs':
memops.c:(.text+0x4dc): undefined reference to `fast_rand'

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>