Use -fvisibility=hidden for spdlog

[johnkerl]

This is a branch coded up by @teo-tsirpanis . I'm putting up a PR for it, at his expicit request.

The problem to be solved is intermittent errors in TileDB-SOMA, which uses this repo as a dependency. For dev work, on a Mac, I build both TileDB Core and TileDB-SOMA from source. The intersection of those three things makes me, perhaps, unusual. Regardless, I have (until this PR) codepaths which, quite simply, always segfault.

The segfaulting patterns involve innocuous logging statements. The stack traces are of this form: https://gist.github.com/johnkerl/b1e07a70906177f498f6e9efa2979376

Notes:

• Note the arrowed lines
• A variable in one frame called formatted is being passed to another with argument name dest
• In lldb, p sizeof(formatted) in the upper frame shows 24 while p sizeof(dest) in the lower frame shows 288
• This is across the boundary from libtiledb.dylib spdlog::logger to libtiledbsoma.dylib spdlog::logger, and back -- so it's an ABI issue apparently.
• I compiled/reran with 1.14.1 for soma & core spdlog both, yet the issue persists

I also tried -fvisibility=hidden within TileDB-SOMA's copy of spdlog and was not able to resolve the problem. Meanwhile @teo-tsirpanis's solution here does resolve the problem.

[sc-62143]

---

TYPE: IMPROVEMENT
DESC: Use -fvisibility=hidden for spdlog

[teo-tsirpanis]

Thanks! gabime/spdlog#3322 will fix the issue upstream.

[johnkerl]

@teo-tsirpanis @ihnorton thank you for your approval!

I have no merge permissions on this repo -- please merge if you're OK with merging.

[johnkerl]

Thank you @teo-tsirpanis !