uClibc: add signal info for seccomp related SIGSYS

uClibc: add signal info for seccomp related SIGSYS

uClibc doesn't define signal info for the SIGSYS signal which is issued
in case of hitting a syscall prohibited by seccomp.
This is sad as it makes debugging seccomp filter policies impossible on
some architectures (at least ARM and PowerPC, maybe also others) which
do not coincidentally set si_value.sival_int as the syscall number.

To fix this, import the definitions and macros needed from glibc.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@45720 3c298f89-4303-0410-b956-a3cf2f4a3e73