Remove uses of matches!() macro, incompatible with Firefox build.

When we vendor Cranelift into Firefox, we need to be able to build with
the Firefox CI setup (unless we carry patches on top of upstream).
Unfortunately, the Firefox CI currently appears to build with a slightly
older version of Rust: I can't work out which version exactly, but one
without stable support for `matches!()`.

A recent attempt to version-bump Cranelift failed with build errors at
the two locations in this patch:

https://treeherder.mozilla.org/logviewer.html#/jobs?job_id=305994046&repo=autoland&lineNumber=24829

I also see a bunch of uses of `matches!()` in Peepmatic, but those
crates are not built by Firefox, so we can leave them be for now, I
think.

cranelift/codegen/src/ir/instructions.rs

@@ -311,7 +311,7 @@ impl InstructionData {
                 arg: _,
                 imm,
             } => {
-                if matches!(opcode, Opcode::SdivImm | Opcode::SremImm) {
+                if *opcode == Opcode::SdivImm || *opcode == Opcode::SremImm {
                     imm.sign_extend_from_width(bit_width);
                 }
             }