Note that SrcMgr::SLocEntry's are POD-like, so SmallVector can do a
better job with them. Shaves off 0.7% of -fparse-only time for a
modules test case. Sure makes you wonder...


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@173689 91177308-0d34-0410-b5e6-96231b3b80d8