Dependencies on the rust toolchain

[Hauke Fath <hauke%Espresso.Rhein-Neckar.DE@localhost>]

Sigh... it's one of those days.

Using a couple of round tuits to work on mrtg*, I found that this 
package, which was well-suited to a small monitoring host, all of a 
sudden wants to build this week's lang/rust.

mrtg depends on graphics/gd depends (via default option) on 
graphics/libimagequant, whose DESCR says

Small, portable C library for high-quality conversion of RGBA images to 
8-bit
indexed-color (palette) images.

which may have been true but isn't any more:

<snip>
libimagequant v2 used to be a C library. libimagequant v4 is written 
entirely in Rust, but still exports the same C interface for C 
programs. You will need to install Rust 1.60+ to build it, and adjust 
your build commands. If you do not want to upgrade, you can keep using 
the C version of the library in the 2.x branch of the repo.
</snip>

Given the weight and churn of Rust, I do think we should not blindly 
upgrade utility libraries to Rusted versions, especially when - as in 
this case - there is a non-rust alternative.

I am inclined to make the libimagequant option for graphics/gd 
non-mandatory. And/or package libimagequant v2.

Thoughts?

Cheerio,
Hauke


* <https://github.com/oetiker/mrtg/issues/105>

-- 
Hauke Fath                        <hauke%Espresso.Rhein-Neckar.DE@localhost>
Linnéweg 7
64342 Seeheim-Jugenheim
Germany