Darwin has a bug which affects the use of poll() with a tty fd,
which affects gambit's REPL when at a console, causing 100% CPU
usage.
Gambit recommends this is disabled on Darwin.
Refactor the build rule:
- Put files in $out/gambit instead of $out.
- Make the optimization setting easy to override.
- Make use of gccStdenv more explicit at this level.
- Support new-style runtime options for forcing UTF-8 I/O.
- Override the PACKAGE_VERSION and PACKAGE_STRING with git version.
- Note that the license is lgpl21, not lpgl2 (Note: also dual asl20).
- Try and fail to meaningfully add missing runtimeDeps.
- Build using NIX_BUILD_CORES.
Use -Os rather than -O2 as our compilation flag, document why.
Document why we always use gcc over clang.
Fix openssl path in gambit.
Stop trying to make static openssl.
