This reverts commit 0a944b345e, reversing
changes made to 61733ed6cc.
I dislike these massive stdenv changes with unclear motivation,
especially when they involve gratuitous mass renames like NIX_CC ->
NIX_BINUTILS. The previous such rename (NIX_GCC -> NIX_CC) caused
months of pain, so let's not do that again.
Also updates beta, nightly, nightlyBin, and bootstrap compilers.
Also updates the registry.
Also consolidates logic between bootstrap and nightlyBin compilers.
Also contains some miscellaneous cleanups.
Also patches firefox to build with the newer cargo