When trying to upgrade @llvm.x86.sse2.psrl.dq while parsing a module,
BitcodeReader adds the function to its worklist twice, resulting in a
crash when accessing it the second time.
This patch replaces the worklist vector by a map.
Patch by Philip Pfaffe.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@241281 91177308-0d34-0410-b5e6-96231b3b80d8
