* Fix RELRO load-segment congruence
* Anchor RELRO at its first section, not only .data.rel.ro
lld drops an empty .data.rel.ro, so a program without relocated read-only
data (the Hello World template included) starts RELRO at the GOT or an
initializer array. Requiring .data.rel.ro made the converter reject such
programs with "lacks required section .data.rel.ro".
Anchor the RELRO file offset at the section that begins the region, which
is .data.rel.ro whenever lld keeps it, keep the 16 KiB load congruence
check, and add a host regression that links both shapes with clang/lld
and converts them.
Claude-Session: https://claude.ai/code/session_01N9Vgy2rufAMyibwZgrc86w