package/gdb: fix build of 8.0.1 with glibc 2.29

Between glibc 2.28 and glibc 2.29, commit
89983cb37c9319806a551e8fe9f3a11ff8f973e1 ("Update siginfo constants
from Linux kernel (bug 21286)") was merged. This commit moved the
TRAP_HWBKPT definition from an IA64-specific header to an
architecture-agnostic header.

This change exhibited a build issue that until then was only visible
on IA64 (which Buildroot does not support). This Buildroot commit
backports a patch from gdb upstream (which is in gdb since 8.2) which
mentions IA64 because it was originally meant to fix only the
IA64-related issue. But the glibc change, this change has become
visible on all architectures.

Fixes:
 - No autobuilder failures

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>