kbuild: Add '.rel.*' strip pattern for vmlinux

Prior to binutils commit c12d9fa2afe ("Support objcopy
--remove-section=.relaFOO") [1] in 2.32, stripping relocation sections
required the trailing period (i.e., '.rel.*') to work properly.

After commit 3e86e4d7 ("kbuild: keep .modinfo section in
vmlinux.unstripped"), there is an error with binutils 2.31.1 or earlier
because these sections are not properly removed:

  s390-linux-objcopy: st6tO8Ev: symbol `.modinfo' required but not present
  s390-linux-objcopy:st6tO8Ev: no symbols

Add the old pattern to resolve this issue (along with a comment to allow
cleaning this when binutils 2.32 or newer is the minimum supported
version). While the aforementioned kbuild change exposes this, the
pattern was originally changed by commit 71d815bf ("kbuild: Strip
runtime const RELA sections correctly"), where it would still be
incorrect with binutils older than 2.32.

Fixes: 71d815bf ("kbuild: Strip runtime const RELA sections correctly")
Link: https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=c12d9fa2afe7abcbe407a00e15719e1a1350c2a7

 [1]
Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
Closes: https://lore.kernel.org/CA+G9fYvVktRhFtZXdNgVOL8j+ArsJDpvMLgCitaQvQmCx=hwOQ@mail.gmail.com/


Acked-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Alexey Gladkov <legion@kernel.org>
Acked-by: Nicolas Schier <nsc@kernel.org>
Link: https://patch.msgid.link/20251008-kbuild-fix-modinfo-regressions-v1-2-9fc776c5887c@kernel.org


Signed-off-by: Nathan Chancellor <nathan@kernel.org>