Turn off LTO for dev and test builds.

[mikebenfield]

This results in a penalty to full compilation time, but a dramatic speedup to partial recompilation time.

[mikebenfield]

On my system, on this branch:

% cargo clean
...
% cargo build --profile dev
...
    Finished `dev` profile [optimized + debuginfo] target(s) in 7m 52s

% touch compiler/parser/src/lib.rs
% cargo build --profile dev
...
    Finished `dev` profile [optimized + debuginfo] target(s) in 6.84s

% touch compiler/passes/src/lib.rs
% cargo build --profile dev
...
    Finished `dev` profile [optimized + debuginfo] target(s) in 5.76s

That is, a full compile takes about 8 minutes, and a partial recompile takes about 6 seconds.

On the mainnet branch, those times are 6 minutes and 4 minutes.

[d0cd]

LGTM!