Merge the `use` parts of the `no_std` branch. This reduces the diffs
between master and the `no_std` branch, making it easier to maintain.
Most of these changes are derived from patches by @lachlansneff in
https://github.com/Cretonne/cretonne/tree/no_std.
This allows the assertions to be disabled in release builds, so that
the code is faster and smaller, at the expense of not performing the
checks. Assertions can be re-enabled in release builds with the
debug-assertions flag in Cargo.toml, as the top-level Cargo.toml
file does.
Rename the ArgumentType type to AbiParam since it describes the ABI
characteristics of a parameter or return value, not just the value type.
In Signature, rename members argument_types and return_types to "params"
and "returns". Again, they are not just types.
Fix a couple lingering references to "EBB arguments".
The word "scalar" is a bit vague and tends to mean "non-vector". Since
we are about to add new CPU flag value types that can't appear as vector
lanes, make the distinction clear: LaneType represents value types that
can appear as a vector lane.
Also replace the Type::is_scalar() method with an is_vector() method.
Insert conversion code that reconstructs the original function argument
types from the legalized ABI signature.
Add abi::legalize_abi_value(). This function is used when adapting code
to a legalized function signature.
Add an abi module with code that is probably useful to all ISAs when
implementing this function.
Add a unit() method to RegClassData which can be used to index the
register units in a class.
