Use temporary directory for intermediate .ll files

[xoxorwr]

Most systems are configred so that /tmp is essentially a ramdisk, so this PR:

• reduces unnecessary disk i/o and wear on SSDs (~30mb on my project everytime i save for hotreload)
• speeds up optimization and linking phases

This is basically a copy paste of lb_filepath_obj_for_module's logic

[laytan]

Does -keep-temp-files keep the old behavior?

[xoxorwr]

Does -keep-temp-files keep the old behavior?

Yes, behavior remain unchanged, it just change the direectory

I should add that this PR should be tested on Windows, I don't have a windows machine with me right now

[gingerBill]

Yes, behavior remain unchanged, it just change the direectory

As silly as this sounds but that is changing the behaviour though.

I recommend allowing a way to opt-out of the directory behaviour is possible, and not just put it in a random /tmp directly. The point of stuff of the command -keep-temp-files is to be able to easily inspect where things went wrong, so placing it in a hard to find temp directory isn't a good idea.