This commit adds a procedural macro which can be used to test instruction
generation in a lightweight way. The intention is that all functions are
annotated with:
#[cfg_attr(test, assert_instr(maxps))]
fn foo(...) {
// ...
}
and then during `cargo test --release` it'll assert the function `foo` does
indeed generate the instruction `maxps`. This only activates tests in optimized
mode to avoid debug mode inefficiencies, and it uses a literal invocation of
`objdump` and some parsing to figure out what instructions are inside each
function. Finally it also uses the `backtrace` crate to figure out the symbol
name of the relevant function and hook that up to the output of `objdump`.
I added a few assertions in the `sse` module to get some feedback, but curious
what y'all think of this!
