https://github.com/thepowersgang/mrustc/issues/109
From: Danny Milosavljevic <dannym@scratchpost.org>
Date: Fri, 3 Jan 2019 13:00:00 +0100

--- mrustc/src/expand/proc_macro.cpp.orig	2019-02-01 14:16:54.208486062 +0100
+++ mrustc/src/expand/proc_macro.cpp	2019-02-01 14:17:14.350925705 +0100
@@ -977,7 +977,7 @@
     for(;;)
     {
         auto b = recv_u8();
-        v |= static_cast<uint64_t>(b) << ofs;
+        v |= static_cast<uint64_t>(b & 0x7F) << ofs;
         if( (b & 0x80) == 0 )
             break;
         ofs += 7;