Detect and error helpfully when neither use-installed-tools or use-compiled-tools are enabled on rustc_codegen_spirv

[fu5ha]

Right now, we get a fairly unhelpful error originating within the spirv-tools crate that is actually caused by neither of these features being enabled. Should be possible to do a

#[cfg(none(feature = "use-installed-tools", feature = "use-compiled-tools"))]
error!("Enable one of the `use-compiled-tools` or `use-installed-tools` features");

or something to that effect

[DJMcNab]

I think ideally this would be in a dependency of spirv-tools, because then the error would happen before any compilation errors due to those missing.

[XAMPPRocky]

I'm currently working changes to the build system that will remove the need for this, as we'll be able to detect whether you have installed tools or not, and build with the appropriate feature.

[khyperia]

The relevant code for the error message @termhn discussed is now in spirv-tools-rs, so, transferred it here.