Switch crosstool-ng configure scripts to xtask.

[Alexhuszagh]

Rewrite the bash build scripts to Rust, allowing a better CLI interface, easier maintenance, and better help messages via clap.

[Alexhuszagh]

This is related to the discussion here.

[Emilgardis]

I feel like all the if statements here on major and minor can be combined into a match (minor, major) with either range patterns or if guards.

[Alexhuszagh]

I think that's somewhat difficult, since there's no fallthrough cases (the only time this is actually valuable):

if gcc_major > 4 || (gcc_major == 4 && gcc_major > 9) {
    ct_gcc.push_str("\nCT_GCC_later_than_4_9=y");
}
if gcc_major > 4 || (gcc_major == 4 && gcc_major >= 9) {
    ct_gcc.push_str("\nCT_GCC_4_9_or_later=y");
}
if gcc_major > 4 || (gcc_major == 4 && gcc_major > 8) {
    ct_gcc.push_str("\nCT_GCC_later_than_4_8=y");
}
if gcc_major > 4 || (gcc_major == 4 && gcc_major >= 8) {
    ct_gcc.push_str("\nCT_GCC_4_8_or_later=y");
}

Would become:

match (gcc_major, gcc_major) {
    (5.., _) | (4, 10..) => {
        ct_gcc.push_str("\nCT_GCC_later_than_4_9=y");
        ct_gcc.push_str("\nCT_GCC_4_9_or_later=y");
        ct_gcc.push_str("\nCT_GCC_later_than_4_8=y");
        ct_gcc.push_str("\nCT_GCC_4_8_or_later=y");
    },
    (4, 9) => {
        ct_gcc.push_str("\nCT_GCC_4_9_or_later=y");
        ct_gcc.push_str("\nCT_GCC_later_than_4_8=y");
        ct_gcc.push_str("\nCT_GCC_4_8_or_later=y");
    }
    (4, 8) => {
        ct_gcc.push_str("\nCT_GCC_4_8_or_later=y");
    }
    _ => (),
}

These aren't exclusive if statements, they each run sequentially. I guess we could have an external helper function?

let push_ge_49 = |output: &mut String| {
    ct_gcc.push_str("\nCT_GCC_4_9_or_later=y");
    ct_gcc.push_str("\nCT_GCC_later_than_4_8=y");
    ct_gcc.push_str("\nCT_GCC_4_8_or_later=y");
};

match (gcc_major, gcc_major) {
    (5.., _) | (4, 10..) => {
        ct_gcc.push_str("\nCT_GCC_later_than_4_9=y");
        push_ge_49(&mut ct_gcc);
    },
    (4, 9) => {
        push_ge_49(&mut ct_gcc);
    }
    (4, 8) => {
        ct_gcc.push_str("\nCT_GCC_4_8_or_later=y");
    }
    _ => (),
}

But I still don't think that's better.

[Emilgardis]

I dislike the repetitive if blocks, but that just leaves more room for improvement, and if it works it works. LGTM!

bors r+

[bors]

Build succeeded:

• conclusion