`#pragma GCC visibility push(hidden)' results in free() symbol being .hidden,
and linker woes. As a remedy, temporarily revert visibility to default when
including this header (probably not the best way to solve the problem though).
While here, pacify portlint(1) by removing hard-coded shlib ABI versions in
LIB_DEPENDS.
Reported by: pointyhat (via pav, erwin)
