winch(x64): Improve ABI support in trampolines (#6204)

This commit improves ABI support in Winch's trampolines mainly by:

* Adding support for the `fastcall` calling convention.
* By storing/restoring callee-saved registers.

One of the explicit goals of this change is to make tests available in the x86_64 target
as a whole and remove the need exclude the windows target.

This commit also introduces a `CallingConvention` enum, to better
reflect the subset of calling conventions that are supported by Winch.

winch/codegen/src/isa/aarch64/mod.rs

@@ -3,7 +3,7 @@ use crate::{
     abi::ABI,
     codegen::{CodeGen, CodeGenContext},
     frame::{DefinedLocals, Frame},
-    isa::{Builder, TargetIsa},
+    isa::{Builder, CallingConvention, TargetIsa},
     masm::MacroAssembler,
     regalloc::RegAlloc,
     regset::RegSet,
@@ -92,7 +92,7 @@ impl TargetIsa for Aarch64 {
         let mut masm = Aarch64Masm::new(self.shared_flags.clone());
         let stack = Stack::new();
         let abi = abi::Aarch64ABI::default();
-        let abi_sig = abi.sig(sig);
+        let abi_sig = abi.sig(sig, &CallingConvention::Default);
 
         let defined_locals = DefinedLocals::new(&mut body, validator)?;
         let frame = Frame::new(&abi_sig, &defined_locals, &abi)?;