Add str::split_ascii_whitespace.
As mentioned in #48656.
While `str::split_whitespace` now works in `libcore`, it still makes sense to offer this method, considering how it is still more performant in cases where only ASCII is necessary.
[fuchsia] Update zx_cprng_draw to target semantics
This change is the final step in improving the semantics of
zx_cprng_draw. Now the syscall always generates the requested number of
bytes. If the syscall would have failed to generate the requested number
of bytes, the syscall either terminates the entire operating system or
terminates the calling process, depending on whether the error is a
result of the kernel misbehaving or the userspace program misbehaving.
This change is the final step in improving the semantics of
zx_cprng_draw. Now the syscall always generates the requested number of
bytes. If the syscall would have failed to generate the requested number
of bytes, the syscall either terminates the entire operating system or
terminates the calling process, depending on whether the error is a
result of the kernel misbehaving or the userspace program misbehaving.
Implement `#[macro_export(local_inner_macros)]` (a solution for the macro helper import problem)
Implement a solution for the macro helper issue discussed in https://github.com/rust-lang/rust/issues/35896 as described in https://github.com/rust-lang/rust/issues/35896#issuecomment-395977901.
Macros exported from libraries can be marked with `#[macro_export(local_inner_macros)]` and this annotation changes how nested macros in them are resolved.
If we have a fn-like macro call `ident!(...)` and `ident` comes from a `macro_rules!` macro marked with `#[macro_export(local_inner_macros)]` then it's replaced with `$crate::ident!(...)` and resolved as such (`$crate` gets the same context as `ident`).
