rustc_target: Further cleanup use of target options
Follow up to https://github.com/rust-lang/rust/pull/77729.
Implements items 2 and 4 from the list in https://github.com/rust-lang/rust/pull/77729#issue-500228243.
The first commit collapses uses of `target.options.foo` into `target.foo`.
The second commit renames some target options to avoid tautology:
`target.target_endian` -> `target.endian`
`target.target_c_int_width` -> `target.c_int_width`
`target.target_os` -> `target.os`
`target.target_env` -> `target.env`
`target.target_vendor` -> `target.vendor`
`target.target_family` -> `target.os_family`
`target.target_mcount` -> `target.mcount`
r? `@Mark-Simulacrum`
inliner: Use substs_for_mir_body
Changes from 68965 extended the kind of instances that are being
inlined. For some of those, the `instance_mir` returns a MIR body that
is already expressed in terms of the types found in substitution array,
and doesn't need further substitution.
Use `substs_for_mir_body` to take that into account.
Resolves#78529.
Resolves#78560.
with an eye on merging `TargetOptions` into `Target`.
`TargetOptions` as a separate structure is mostly an implementation detail of `Target` construction, all its fields logically belong to `Target` and available from `Target` through `Deref` impls.
Changes from 68965 extended the kind of instances that are being
inlined. For some of those, the `instance_mir` returns a MIR body that
is already expressed in terms of the types found in substitution array,
and doesn't need further substitution.
Use `substs_for_mir_body` to take that into account.
This required another custom driver to ensure that build scripts are
built using cg_llvm instead of cg_clif.
After this change only rustdoc still uses -Zcodegen-backend
Benchmark #1: ./raytracer_cg_clif_pre
Time (mean ± σ): 8.251 s ± 0.021 s [User: 8.245 s, System: 0.005 s]
Range (min … max): 8.225 s … 8.292 s 10 runs
Benchmark #2: ./raytracer_cg_clif_post
Time (mean ± σ): 8.206 s ± 0.043 s [User: 8.199 s, System: 0.007 s]
Range (min … max): 8.168 s … 8.279 s 10 runs
