[libc] Implement wmemset

[michaelrj-google]

Described in C23 (page 458): https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3220.pdf#page=458

wmemset sets an array of widechars to a specific value.

Here's a checklist for what you'll need to do for this:

• Add the implementation of wmemset in /src/wchar
• Add tests for wmemset in /test/src/wchar
• Add wmemset to entrypoints.txt for at least x86_64 and whatever you're building on
• Add wmemset to include/wchar.yaml

(Reserved for specific assignee)

[llvmbot]

@llvm/issue-subscribers-libc

Author: Michael Jones (michaelrj-google)

Described in C23 (page 458): https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3220.pdf#page=458

wmemset sets an array of widechars to a specific value.

Here's a checklist for what you'll need to do for this:

• Add the implementation of wmemset in /src/wchar
• Add tests for wmemset in /test/src/wchar
• Add wmemset to entrypoints.txt for at least x86_64 and whatever you're building on
• Add wmemset to include/wchar.yaml

(Reserved for specific assignee)

[uzairnawaz]

I can complete this one!

[michaelrj-google]

completed in #141691