LLVM does not support host feature detection (only host cpu
detection) on apple platforms. As such, the returned feature
string will be empty. Adding this empty string to the target-features
attribute results in a verifier error on LLVM 22.
Fix this by not adding the empty string to the target features.
The reason why this was not caught by the target-cpu-native test
is that it requires a function that adds *some* target features,
otherwise the attribute is omitted entirely. We achieve this with
a somewhat peculiar construction that enables `neon` if it's
already enabled. (This is to avoid enabling it on softfloat targets.)
With the exception of `tests/run-make/translation/test.rs`, which has a
syntax error.
The expected output in `rustdoc-error-lines/rmake.rs`'s required slight
tweaking.
The two `reproducible-build.rs` files need `// ignore-tidy-linelength`
because rustfmt produces lines longer than 100 chars, which tidy doesn't
like, yuk.
Nikita Popov