Optimize codegen slightly calling wasm functions

Currently wasm-calls work with `Result<T, Trap>` internally but `Trap`
is an enum defined in `wasmtime-runtime` which is actually quite large.
Since traps are supposed to be rare this commit changes these functions
to return a `Box<Trap>` which is un-boxed later up in the `wasmtime`
crate within a `#[cold]` function.

crates/runtime/src/traphandlers/macos.rs

@@ -409,7 +409,8 @@ unsafe extern "C" fn unwind(wasm_pc: *const u8) -> ! {
 /// unhandled thread-level exceptions get automatically forwarded to the
 /// task-level port which is where we'd expected things like breakpad/crashpad
 /// exception handlers to get registered.
-pub fn lazy_per_thread_init() -> Result<(), Trap> {
+#[cold]
+pub fn lazy_per_thread_init() -> Result<(), Box<Trap>> {
     unsafe {
         assert!(WASMTIME_PORT != MACH_PORT_NULL);
         let this_thread = mach_thread_self();