Fix infinite recursion at the end of a file

Author: DougGregor

lib/Parse/ParseDecl.cpp

@@ -4346,8 +4346,8 @@ bool Parser::isStartOfSwiftDecl(bool allowPoundIfAttributes) {
   if (Tok.is(tok::pound_if) && allowPoundIfAttributes) {
     BacktrackingScope backtrack(*this);
     bool sawAnyAttributes = false;
-    return skipIfConfigOfAttributes(sawAnyAttributes) && sawAnyAttributes &&
-        isStartOfSwiftDecl();
+    return skipIfConfigOfAttributes(sawAnyAttributes) &&
+        (Tok.is(tok::eof) || (sawAnyAttributes && isStartOfSwiftDecl()));
   }
 
   // If we have a decl modifying keyword, check if the next token is a valid

lib/Parse/ParseIfConfig.cpp

@@ -962,6 +962,10 @@ bool Parser::skipIfConfigOfAttributes(bool &sawAnyAttributes) {
       break;
   }
 
+  // If we ran out of tokens, say we consumed the rest.
+  if (Tok.is(tok::eof))
+    return true;
+
   return Tok.isAtStartOfLine() && consumeIf(tok::pound_endif);
 }