systemtap: Fix headers issue with x86 and 5.13 headers

On some x86 platforms there were header issues causing pt_regs compile
failures for our stap tests, e.g. on genericx86-64 but not qemux86-64.

Backport a patch from upstream which fixes the issue.

[YOCTO #14491]

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>