wasmtime: Collect stack pointer during traps

Nothing uses this yet but I want to get collection of this register
right on our many supported platforms before introducing the changes
that need it.

Author: jameysharp

crates/wasmtime/src/runtime/vm/sys/unix/signals.rs

@@ -270,6 +270,7 @@ unsafe fn get_trap_registers(cx: *mut libc::c_void, _signum: libc::c_int) -> Tra
             TrapRegisters {
                 pc: cx.uc_mcontext.gregs[libc::REG_RIP as usize] as usize,
                 fp: cx.uc_mcontext.gregs[libc::REG_RBP as usize] as usize,
+                sp: cx.uc_mcontext.gregs[libc::REG_RSP as usize] as usize,
             }
         } else if #[cfg(all(target_os = "linux", target_arch = "x86"))] {
             let cx = &*(cx as *const libc::ucontext_t);

crates/wasmtime/src/runtime/vm/traphandlers.rs

@@ -34,6 +34,7 @@ pub use traphandlers::SignalHandler;
 pub(crate) struct TrapRegisters {
     pub pc: usize,
     pub fp: usize,
+    pub sp: usize,
 }
 
 /// Return value from `test_if_trap`.