elfcopy/strip: Ensure sections have required alignment on output

Object files may specify insufficient alignment on certain sections, for
example due to a bug in NASM[1]. When we detect that case in elfcopy or
strip, emit a warning and increase the alignment to the minimum
required.

The NASM bug was fixed in 2015[2], but we might as well have this fixup
(and warning) in elfcopy in case we encounter such a file for any other
reason.

This might be reworked somewhat upstream - see ELF Tool Chain
ticket 485[3].

[1] https://bugzilla.nasm.us/show_bug.cgi?id=3392307
[2] https://repo.or.cz/w/nasm.git/commit/1f0cb0f2c1ba632c0fab02424928cfb756a9160c
[3] https://sourceforge.net/p/elftoolchain/tickets/485/

PR: 198611
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D2292