Increase the size of the sigaltstack. (#1315)

* Increase the size of the sigaltstack.

Rust's stack overflow handler installs a sigaltstack stack with size
SIGSTKSZ, which is too small for some of the things we do in signal
handlers, and as of this writing lacks a guard page. Install bigger
sigaltstack stacks so that we have enough space, and have a guard page.

crates/api/src/trap.rs

@@ -50,6 +50,9 @@ impl Trap {
             wasmtime_runtime::Trap::Wasm { desc, backtrace } => {
                 Trap::new_with_trace(desc.to_string(), backtrace)
             }
+            wasmtime_runtime::Trap::OOM { backtrace } => {
+                Trap::new_with_trace("out of memory".to_string(), backtrace)
+            }
         }
     }