package/libunwind: link to libgcc_s, not libgcc
Backport a fix from upstream to link against libgcc_s instead of libgcc.
Fixes ltrace build failures:
http://autobuild.buildroot.net/results/a0c/
a0c132f8cdea2c34ceff27606764a60c2853f644/
http://autobuild.buildroot.net/results/67f/
67fbd04d6ae187861fa1bf84d3df1877c7be6fb2/
http://autobuild.buildroot.net/results/0ca/
0ca564101b870e5953acb66ac832ce9e23198392/
...
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>