CompileStep.emit_h setting puts headers in unexpected directory for zig build

[leximayfield]

Zig Version

0.11.0-dev.2336+5b82b4004

Steps to Reproduce and Observed Behavior

When creating a static library with zig build, adding emit_h to the CompileStep results in the header being output to the CWD, not the cache directory. This causes the install step to fail because although it knows that it needs to copy a header file, it tries to look in the cache directory and blows up with a FileNotFound.

Here is what I put in my build.zig file:

    var lib = b.addStaticLibrary(.{
        .name = "mercnet",
        .root_source_file = .{ .path = "src/mercnet.zig" },
        .target = target,
        .optimize = optimize,
    });
    lib.emit_h = true;

...and this is the output:

[leximax@DESKTOP-9USQ50S mercnet]$ zig build --verbose
/home/leximax/.opt/zig/zig build-lib -ofmt=c /home/leximax/workspace/mercnet/src/mercnet.zig -femit-h --cache-dir /home/leximax/workspace/mercnet/zig-cache --global-cache-dir /home/leximax/.cache/zig --name mercnet -static --enable-cache --listen=- 
install mercnet: error: unable to update file from '/home/leximax/workspace/mercnet/zig-cache/o/a5f288f5a4f10eb3a43c92bf0db3933c/mercnet.h' to '/home/leximax/workspace/mercnet/zig-out/include/mercnet.h': FileNotFound

It appears that -emit-h could in theory take a path parameter, but none is being passed.

Expected Behavior

No error, header file is installed to the zig-out directory.

[RossComputerGuy]

Looks like the option for the filename isn't even passed to the respective Zig call. Looking at the zig build-lib help output, I think I can make a PR to fix this.