* Put TargetIsa's emit_inst under a "testing_hooks" feature.
In practice, TargetIsa's emit_inst pulls in its own instantiation
of the target-specifi `emit_inst` functions, which can be quite
large, and LTO doesn't eliminate them because they're held live
by TargetIsa's vtable.
Fortunately, this function is only used by tests, so we can put
it behind a feature flag.
Fixes#530.
* Add comments for `emit_inst` to clarify its purpose.
This switches from a custom list of architectures to use the
target-lexicon crate.
- "set is_64bit=1; isa x86" is replaced with "target x86_64", and
similar for other architectures, and the `is_64bit` flag is removed
entirely.
- The `is_compressed` flag is removed too; it's no longer being used to
control REX prefixes on x86-64, ARM and Thumb are separate
architectures in target-lexicon, and we can figure out how to
select RISC-V compressed encodings when we're ready.
* Update to rustfmt-preview.
* Run "cargo fmt --all" with rustfmt 0.4.1.
rustfmt 0.4.1 is the latest release of rustfmt-preview available on the
stable channel.
* Fix a long line that rustfmt 0.4.1 can't handle.
* Remove unneeded commas left behind by rustfmt.
