Auto merge of rust-lang#704 - fitzgen:bitfields-into-ir, r=emilio

Move bitfields into the IR

This PR moves bitfields and the computation of their allocation units into the IR. They were previously computed on-the-fly during code generation. In addition to breaking up and compartmentalizing a portion of the gargantuan `CodeGeneration` implementation for `CompInfo`, this paves the way for adding const-fn bitfield unit constructors.

Also some improvements to `tests/test-one.sh`.

Also some graphviz output improvements that got tangled up in the last commit without a good way to pull them out into their own commit (sorry).

r? @emilio

Author: bors-servo

Cargo.lock

@@ -46,6 +46,7 @@ cexpr = "0.2"
 cfg-if = "0.1.0"
 clang-sys = { version = "0.18.0", features = ["runtime", "clang_3_9"] }
 lazy_static = "0.2.1"
+peeking_take_while = "0.1.2"
 syntex_syntax = "0.58"
 regex = "0.2"
 # This kinda sucks: https://github.com/rust-lang/cargo/issues/1982

Cargo.toml

@@ -3,6 +3,8 @@
 set -xeu
 cd "$(dirname "$0")/.."
 
+export RUST_BACKTRACE=1
+
 # Regenerate the test headers' bindings in debug and release modes, and assert
 # that we always get the expected generated bindings.