Nix reorganization

[enobayram]

This PR turns our Nix configuration somewhat inside out and moves all the heavy lifting to default.nix from flake.nix.

The rationale is that Nix flakes are inflexible by design so that they provide static information about their inputs and their outputs. By moving the interesting logic back to default.nix and importing it from flake.nix we're able to accept arguments to the nix-build call to build our artifacts with parameters.

This PR introduces the dontStrip, threaded and enableProfiling parameters to default.nix.

In order to expose this new flexibility to our chanweb-data-docker images, this PR also inlines docker-legacy.nix into default.nix so that, say, nix-build --arg enableProfiling true -A dockerImage builds a docker image with a CW-D binary built with profiling.

Note that this default.nix still piggy backs on the new nix flakes feature for managing its inputs like haskell.nix and nixpkgs.

[enobayram]

Here are some steps to verify that the various default.nix arguments introduced by this PR work as intended:

The default build

(strips the debug symbols, is threaded and has no profiling)

$ nix log $(nix-build) | grep -e ".\{0,20\}strip" -e ".\{0,10\}threaded.\{0,10\}" -e ".\{0,10\}library-profiling.\{0,10\}" -o
s --flags=threaded --exact-c
--with-ar=ar --with-strip
=strip
--enable-executable-strip
ng --enable-library-strip
--disable-library-profiling --disable
strip
-wrapper-11.3.0/bin/strip
strip
ping (with command strip
strip
-wrapper-11.3.0/bin/strip

The stripped executable size is 16.8MB:

$ du -d0 $(nix-build)
16868	/nix/store/zvjl5p532k53bhxis2wipwgw1nf5nyk3-chainweb-data-exe-chainweb-data-2.1.1

--arg dontStrip true

$ nix log $(nix-build --arg dontStrip true) | grep -e ".\{0,10\}with-strip.\{0,10\}"  -o
h-ar=ar --with-strip=strip --d

Unstripped size is 24.6 MB:

$ du -d0 $(nix-build --arg dontStrip true)
24604	/nix/store/yrj4h59cc6zasrysqjxmm4s8b2qqrlax-chainweb-data-exe-chainweb-data-2.1.1

--arg threaded false

$ nix log $(nix-build --arg threaded false) | grep -e ".\{0,10\}threaded.\{0,10\}" -o
 --flags=-threaded --exact-c

Can't be run threaded:

$ $(nix-build --arg threaded false)/bin/chainweb-data +RTS -N
chainweb-data: the flag -N requires the program to be built with -threaded
...

--arg enableProfiling true

$ nix log $(nix-build --arg enableProfiling true) | grep -e ".\{0,10\}library-profiling.\{0,10\}" -o
 --enable-library-profiling --enable-

[jwiegley]

Clever stuff!