Add --disable-library-profiling option

[locallycompact]

enableLibraryProfiling = true seems to be the default when I use cabal2nix, can we have an explicit option to set it to false?

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I made an alternate fix for this by just explicitly writing the attr instead of boolattr for these options, but further to that opinion I think boolattr is prone to breakage because we can never assume how nixpkgs will interpret a missing key into configure options, so in the interest of discoverability I don't think boolattr is a good idea.

#583

[locallycompact]

Ok I just changed it to make boolattr always write out.