[#3844 + #3767] update std.c and std.os.linux to use null-terminated pointer types

[raulgrell]

Resubmitting the pull request in a separate branch, and as a draft. Apologies for the clutter.

I wasn't sure how to handle the execve function.

error: integer value 0 cannot be coerced to type '[*]const u8'
pub fn execve(path: [*:0]const u8, argv: [*:0]const ?[*]const u8, envp: [*:0]const ?[*]const u8) usize

error: expected type '[*:0]const u8', found 'comptime_int'
pub fn execve(path: [*:0]const u8, argv: [*:0]const [*:0]const u8, envp: [*:0]const [*:0]const u8) usize

Thanks to @fengb I settled on

pub extern "c" fn execve(path: [*:0]const u8, argv: [*:null]const ?[*:0]const u8, envp: [*:null]const ?[*:0]const u8) c_int;

[raulgrell]

zig build test-std -Dskip-release ran with no issues. The full test suite is huge. I was convinced I was doing something wrong until I realized it was my VM that was running out of RAM.

Thanks to @tiehuis for also pointing me to the right signature for execve.

EDIT: Let me know if I should squash the commits

[raulgrell]

Thanks for the speedy review.

In one commit, I left the port cast in. In the next, I added a allocPrintCstr function that returns a null terminated slice. Not sure it's in the right place or if it's the best name.

[daurnimator]

LGTM

[andrewrk]

Still WIP?

[raulgrell]

No longer WIP!