While the KCFI scheme is not incompatible with unwinding, LLVM's
`invoke` instruction does not currently support KCFI bundles. While it
likely will in the near future, we won't be able to assume that in Rust
for a while.
This enables KCFI-based testing for all the CFI run-pass tests in the
suite today. We can add the test header on top of in-flight CFI tests
once they land.
It also enables KCFI as a sanitizer for x86_64 and aarch64 Linux to make
this possible. The sanitizer should likely be available for all aarch64,
x86_64, and riscv targets, but that isn't critical for initial testing.
Previously, we only rewrote `&self` and `&mut self` receivers. By
instantiating the method from the trait definition, we can make this
work work with arbitrary legal receivers instead.
