The new implementation doesn't use weak lang items and instead changes
`#[alloc_error_handler]` to an attribute macro just like
`#[global_allocator]`.
The attribute will generate the `__rg_oom` function which is called by
the compiler-generated `__rust_alloc_error_handler`. If no `__rg_oom`
function is defined in any crate then the compiler shim will call
`__rdl_oom` in the alloc crate which will simply panic.
This also fixes link errors with `-C link-dead-code` with
`default_alloc_error_handler`: `__rg_oom` was previously defined in the
alloc crate and would attempt to reference the `oom` lang item, even if
it didn't exist. This worked as long as `__rg_oom` was excluded from
linking since it was not called.
This is a prerequisite for the stabilization of
`default_alloc_error_handler` (#102318).
In addition to the whole-system emulation/virtualization, QEMU also
supports user-mode emulation, where the emulation happens as a normal
process inside the parent system. This allows running most tests by
simply spawning remote-test-server inside user-mode emulation.
Unfortunately, QEMU always writes its own message in addition to the
system one when a core dump happens, which breaks a few tests which
match on the exact output of the system.
This PR changes those tests to strip the (possible) QEMU output before
checking if the output is expected.
