Fix potential stack overflow for no musttail

Closes #1

src/musttail.h

@@ -6,6 +6,7 @@
 
 #if __has_attribute(musttail)
 #define MUSTTAIL __attribute__((musttail))
+#define HAS_MUSTTAIL
 #else
 #define MUSTTAIL
 #endif

src/parser3.h

@@ -146,6 +146,10 @@ struct Parser3 {
   NumDfa numDfa;
   Utf8Dfa strDfa;
   bool inKey = false;
+
+#ifndef HAS_MUSTTAIL
+  char *stashBufForTrampoline;
+#endif
 };
 
 inline PRESERVE_NONE WeaselJsonStatus skipWhitespace(char *&buf, char *bufEnd) {
@@ -1029,13 +1033,29 @@ constexpr inline struct ContinuationTable {
 
 inline WeaselJsonStatus Parser3::parse(char *buf, int len) {
   this->dataBegin = this->writeBuf = buf;
+
+#ifdef HAS_MUSTTAIL
   return symbolTables.continuations[top()](this, buf, buf + len);
+#else
+  this->stashBufForTrampoline = buf;
+  WeaselJsonStatus result;
+  while ((result = symbolTables.continuations[top()](
+              this, stashBufForTrampoline, buf + len)) == WeaselJsonStatus(-1))
+    ;
+  return result;
+#endif
 }
 
 inline PRESERVE_NONE WeaselJsonStatus Parser3::keepGoing(Parser3 *self,
                                                          char *buf,
                                                          char *bufEnd) {
+#ifdef HAS_MUSTTAIL
   MUSTTAIL return symbolTables.continuations[self->top()](self, buf, bufEnd);
+#else
+  self->stashBufForTrampoline = buf;
+  (void)bufEnd;
+  return WeaselJsonStatus(-1);
+#endif
 }
 
 } // namespace parser3