LTO: clarify why we need to gracefully handle sys::fs::rename failures
LTO: clarify why we need to gracefully handle sys::fs::rename failures

Reviewers: pcc, rafael

Reviewed By: pcc

Subscribers: mehdi_amini, llvm-commits, hiraditya

Differential Revision: https://reviews.llvm.org/D40094

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@318362 91177308-0d34-0410-b5e6-96231b3b80d8

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