package/gdb: fix gdb segfault with Python 3.9 support

package/gdb: fix gdb segfault with Python 3.9 support

When enabling Python 3 support in gdb < 10, gdb segfaults at startup.

The issue is was resolved by the following upstream gdb commit,
present since gdb 10.1:

    commit c47bae859a5af0d95224d90000df0e529f7c5aa0
    Author: Kevin Buettner <kevinb@redhat.com>
    Date:   Wed May 27 20:05:40 2020 -0700

        Fix Python3.9 related runtime problems
        [...]

This commit backports this fix to all relevant gdb versions supported
in Buildroot.

Signed-off-by: Thomas De Schampheleire <thomas.de_schampheleire@nokia.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>