move zig.h to become an installation file that can be changed at runtime

[andrewrk]

Currently zig.h is embedded into the zig binary like this:

zig/src/link/C.zig

Line 18 in 974af5f

pub const zig_h = @embedFile("C/zig.h");

However, I think it would be more flexible and useful to be able to edit this file without needing to rebuild the compiler.

• figure out a place to put it within lib/
• integrate with the caching system
• load at runtime instead of @embedFile

[matu3ba]

I am looking into this out of personal curiosity how the caching system works. I should have something working until 18./19. June.
got the part of how the Zig cache works: https://gist.github.com/matu3ba/92e5df1166c51b3725dbd04f7ff1cb4e, next is to get the details and implement it.

[matu3ba]

So far only the Zir of the Zig source file and builtin.zig of a file with c backend (-ofmt=c) are cached into the local cache.
Besides that, 447 files are added to the global cache into z/ (Zir files).
(Tested with #11849 and nuking local and global cache)

Can you be more specific how you expect things to be cached?

APPENDUM: The approach is relative straight forward with using the stuff in cmdTranslateC() in main.zig and adding things like in src/glibc.zig.

[nektro]

it would be part of the global cache, he said he wanted it put inside lib/