uclibc: add a missing function member to siginfo.h

Applying an upstream patch to add a missing function member on ia64,
mips and sparc arches.

Upstream patch URL:
   http://git.uclibc.org/uClibc/commit/libc/sysdeps/linux?id=b4e6e61e2f7c6fb4bf59f66efaa74591a2112912

Fixes:
   http://autobuild.buildroot.net/results/fa0/fa03ecc087a4b30df8b0366bb238be3d167a56d9/



Signed-off-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>