Improve error message for non-SIMD scenarios

[Colerar]

Before:

error[E0308]: mismatched types
   --> (**masked**)/src/lib.rs:228:86
    |
228 | fn please_compile_with_a_simd_compatible_cpu_setting_read_the_simdjsonrs_readme() -> ! {}
    |    ----------------------------------------------------------------------------      ^ expected `!`, found `()`
    |    |
    |    implicitly returns `()` as its body has no tail or `return` expression
    |
    = note:   expected type `!`
            found unit type `()`

For more information about this error, try `rustc --explain E0308`.
error: could not compile `simd-json` due to previous error

After:

error: Please compile with a simd compatible cpu setting, read the simdjson README.
   --> (**masked**)/src/lib.rs:229:5
    |
229 |     compile_error!("Please compile with a simd compatible cpu setting, read the simdjson README.");
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: could not compile `simd-json` due to previous error

Much cleaner, without distracting noise.

[Licenser]

I love it, simple and brilliant! I learned something new :) thanks!

[Licenser]

@Colerar it seems like the compiler error always fires for some reason

[Colerar]

Caused by:

Doc-tests simd-json
error: Please compile with a simd compatible cpu setting, read the simdjson README.
   --> /home/runner/work/simd-json/simd-json/src/lib.rs:229:5
    |
229 |     compile_error!("Please compile with a simd compatible cpu setting, read the simdjson README.");
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: aborting due to previous error

error: doctest failed, to rerun pass `--doc`

Related issues:

rust-lang/cargo#4737
rust-lang/rust#43031

[Colerar]

We need to specify rustdocflags option, as described in: rust-lang/cargo#6650 (comment)

[Licenser]

Great find :) lets give it a try

[Licenser]

Worked perfectly, thanks again! :D