Always inline check in `assert_unsafe_precondition` with cfg(debug_assertions)

The current complexities in `assert_unsafe_precondition` are delicately
balancing several concerns, among them compile times for the cases where
there are no debug assertions. This comes at a large runtime cost when
the assertions are enabled, making the debug assertion compiler a lot
slower, which is very annoying.

To avoid this, we always inline the check when building with debug
assertions.

Numbers (compiling stage1 library after touching core):
- master: 80s
- just adding `#[inline(always)]` to the `cfg(bootstrap)`
  `debug_assertions`: 67s
- this: 54s

So this seems like a good solution. I think we can still get
the same run-time perf improvements for other users too by
massaging this code further (see my other PR about adding
`#[rustc_no_mir_inline]`) but this is a simpler step that
solves the imminent problem of "holy shit my rustc is sooo slow".

Funny consequence: This now means compiling the standard library with
dbeug assertions makes it faster (than without, when using debug
assertions downstream)!

0 files changed, 0 insertions, 0 deletions