WASI,libc: fix libstd with wasi-libc linkage, and enable tests.

[mathetake]

This PR modifies libstd for WASI + wasi-libc target, and resolves #8845

[mathetake]

finally resolved the symbol issue but weird.. I see "the number of locals exceeds the minimum".. look into this now though it looks like a calling convention mismatch..

Error: failed to run main module `/home/mathetake/zig/zig-cache/o/3f9eec2bc857dd8c7327f378ef491e47/test.wasm`

Caused by:
    0: WebAssembly failed to compile
    1: WebAssembly translation error
    2: Invalid input WebAssembly code at offset 14965884: locals exceed maximum
error: the following test command failed with exit code 1:
wasmtime --dir=. /home/mathetake/zig/zig-cache/o/3f9eec2bc857dd8c7327f378ef491e47/test.wasm /home/mathetake/zig/build/zig
The following command exited with error code 1:
/home/mathetake/zig/build/zig test /home/mathetake/zig/lib/std/std.zig -lc --test-name-prefix std-wasm32-wasi-Debug-c-single  --single-threaded --cache-dir /home/mathetake/zig/zig-cache --global-cache-dir /home/mathetake/.cache/zig --name test -target wasm32-wasi --test-cmd wasmtime --test-cmd --dir=. --test-cmd-bin -I /home/mathetake/zig/test --zig-lib-dir /home/mathetake/zig/lib 
error: the following build command failed with exit code 1:
/home/mathetake/zig/zig-cache/o/50a49ecd131d5c652f1182575d182f4d/build /home/mathetake/zig/build/zig /home/mathetake/zig /home/mathetake/zig/zig-cache /home/mathetake/.cache/zig test-std -Dtarget=wasm32-wasi -Denable-wasmtime

[mathetake]

OK a bit of progress.. looks like linking with libc has not succeeded yet.

$ wasm-objdump /home/mathetake/zig/zig-cache/o/3f9eec2bc857dd8c7327f378ef491e47/test.wasm --section=import -x
...
 - func[6] sig=6 <exit|c> <- c.exit
 - func[7] sig=0 <malloc|c> <- c.malloc
 - func[8] sig=6 <free|c> <- c.free
 - func[9] sig=8 <write|c> <- c.write

[mathetake]

looks like we have to remove "c" from here https://github.com/ziglang/zig/blob/master/lib/std/c.zig#L71-L86

[mathetake]

OK now zig-bootstrap/out/host/bin/zig build-exe main.zig -lc --single-threaded -target wasm32-wasi has started working!

const std = @import("std");
pub fn main() void {
    std.debug.print("hello with libc!", .{});
}

[mathetake]

@kubkon I believe this is ready for review. I would appreciate it if you could have a chance to take a look! :)

[mathetake]

Almost there, but the fs tests haven't passed yet. I guess something to do with preopens, but couldn't figure out yet...

[mathetake]

OK finally passes all the tests locally...🤞

[mathetake]

OK I believe everything works now after rebasing 😄 hope all the tests would pass again 🤞

[mathetake]

OK I did a bit of research on wasm-ld behavior on wasm-import-module and wasm-import-name attributes, and other frontend's behavior.. I found that the root cause of linktime symbol mismatch and maybe I could reduce the amount of change (mostly due to the workaround for it) here. Will work on a separate PR in next few days.

[mathetake]

#9279 will reduce the fair amount of change in this PR.

[mathetake]

rebased on #9279 .

[kubkon]

If you don't mind, I'll convert this PR into a draft since it's blocked by #9279 so that we don't merge it prematurely.

[mathetake]

Right, thanks for doing that for me!

[kubkon]

@mathetake could you rebase/merge against master given that #9279 is now merged, and mark the PR as ready for review (if you still feel it's ready ofc!)?

[mathetake]

@kubkon I've just made this for ready again:) Thanks!

[kubkon]

Thanks for addressing the previous set of suggestions, and I apologise for not spending more time on reviewing this PR earlier. Anyway, looks good! I've just got a final set of changes I'd like you to incorporate and we should be ready to merge!

[kubkon]

Suggested change

	if (builtin.target.os.tag != .wasi) {
	if (!has_flock_open_flags and flags.lock != .None) {
	if (!has_flock_open_flags and flags.lock != .None and builtin.target.os.tag != .wasi) {

I think we can put all checks in one if.

[mathetake]

yeah this is a little bit trick.. we need to remove out this if block since since the expression is not compiltime-known, and WASI doesn't have os.flock that's why I put the OS check prior to the if block. Added comment about this: 68617c9

[kubkon]

Ah gotcha, makes sense!

[mathetake]

Thanks @kubkon always! I hope I addressed all your comments:)