Various warnings are emitted when building in Darwin environments,
apparently due to the use of Clang as opposed to GCC. We could continue
to add more `-Wno-xxx` flags as they arise, either with the existing
`stdenv.isDarwin` condition or with the more correct
`stdenv.cc.isClang`, but for an older codebase it seems more prodent to
stick with the latest standard where it builds cleanly. The newer
`-std=c++11` was also attempted, but it still failed to build.
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