Avoid temporary vector for sorting in BitcodeWriter

As suggested by Duncan, fixup for r269634 and r269635

From: Mehdi Amini <mehdi.amini@apple.com>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@269715 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed