Initial reorg.

This is largely the same as #305, but updated for the current tree.

crates/runtime/signalhandlers/Trampolines.cpp

@@ -0,0 +1,37 @@
+#include <setjmp.h>
+
+#include "SignalHandlers.hpp"
+
+extern "C"
+int WasmtimeCallTrampoline(void *vmctx, void (*body)(void*, void*), void *args) {
+  jmp_buf buf;
+  void *volatile prev;
+  if (setjmp(buf) != 0) {
+    LeaveScope(prev);
+    return 0;
+  }
+  prev = EnterScope(&buf);
+  body(vmctx, args);
+  LeaveScope(prev);
+  return 1;
+}
+
+extern "C"
+int WasmtimeCall(void *vmctx, void (*body)(void*)) {
+  jmp_buf buf;
+  void *volatile prev;
+  if (setjmp(buf) != 0) {
+    LeaveScope(prev);
+    return 0;
+  }
+  prev = EnterScope(&buf);
+  body(vmctx);
+  LeaveScope(prev);
+  return 1;
+}
+
+extern "C"
+void Unwind() {
+  jmp_buf *buf = (jmp_buf*) GetScope();
+  longjmp(*buf, 1);
+}