`-Cmin-function-alignment`/`-Calign-functions` support in `rustc`

[ojeda]

i.e. the equivalents of -fmin-function-alignment (GCC, Clang does not support it) / -falign-functions (GCC, Clang).

For the Linux kernel, the behavior wanted is that of GCC's -fmin-function-alignment and Clang's -falign-functions, i.e. align all functions, including cold functions.

There is feature(fn_align), but we need to do it globally.

[ojeda]

@rustbot label I-rust-for-linux

[workingjubilee]

If a feature should be extended with a CLI flag, or at least have its interactions with such a flag considered before landing it, that should be brought up in that issue. Closing as duplicate for now.