The zlib symbols may not be of type 'T' but rather e.g. 'D' -- instead,
tell nm to emit the POSIX format and also to only emit defined symbols,
not undefined ones. Then we just check if the symbol is listed at all,
regardless of type.
We already depend on -U elsewhere (e.g symbolextractor). There's no real
replacement for it, sadly. It's also buggy in some versions of nm, so we
check both its long and short options.
Bug: https://bugs.gentoo.org/938259
Eli Schwartz