Ability to control what Zig emits in build.zig

[jaredramirez]

As far as I understand, right now you can't specify what Zig should emit in build.zig. I'd like to have the equivalent build.zig config for the command: zig build-obj src/main.zig -femit-llvm-ir -fno-emit-bin

Here's what I have in my build.zig

const Builder = @import("std").build.Builder;

pub fn build(b: *Builder) void {
    b.setPreferredReleaseMode(builtin.Mode.ReleaseFast);
    const mode = b.standardReleaseOptions();

    const obj = b.addObject("bitcode", "src/main.zig");
    obj.setBuildMode(mode);

    // Theses don't exist
    // obj.shouldEmitLLVMIR(true);
    // obj.shouldEmitBin(false);

    // test steps, etc
}

After looking in lib/std/build.zig, I think adding something like:

pub fn shouldEmitLLVMIR(self: *LibExeObjStep, should_emit: bool) void {
    self.emit_llvm_ir = should_emit;
}

pub fn shouldEmitBin(self: *LibExeObjStep, should_emit: bool) void {
    self.emit_bin = should_emit;
}

// etc for all other emit types

Then in make everything already seems setup to add the args!

If this is something you'd like, I can submit a PR!

[pfgithub]

You can set obj.emit_llvm_ir = true and obj.emit_bin = true directly already. It would be useful if these had documentation comments though to make it clear that you are supposed to do that.

    const obj = b.addObject("bitcode", "src/main.zig");
    obj.setBuildMode(mode);

    obj.emit_llvm_ir = true;
    obj.emit_bin = true;