adding arc4random* api family for solarish.

[devnexen]

solaris
illumos

[rustbot]

r? @tgross35

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[rustbot]

Some changes occurred in solarish module

cc @jclulow, @pfmooney

[devnexen]

@rustbot label stable-nominated

[RalfJung]

This would help remove a FIXME in std.

Relevant platform docs:

• https://www.illumos.org/man/3C/arc4random
• https://docs.oracle.com/cd/E88353_01/html/E37843/arc4random-3c.html

[tgross35]

Thanks for linking the docs. LGTM but I'll wait for one of the solarish people to double check this, or merge it in another day or two if we don't hear back.

[RalfJung]

@devnexen maybe you can add the docs link to the PR description, so they become part of the commit message.

(As I already told you in multiple past PRs, please write descriptions for your PRs! It makes them much easier to review, and therefore much more likely to be landed. It is not a great practice to throw a piece of code over the fence without saying a single sentence about the what and why and how.)