package/gdb: fix build of 8.1.1 since the bump to 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:

 - http://autobuild.buildroot.org/results/a81eb395bd95306fcbb07c1443c9134fd63fa379



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