Rename fs::GetUniqueID to fs::getUniqueID to match the style guide.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@184431 91177308-0d34-0410-b5e6-96231b3b80d8
Remove the transitional GetUniqueID.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@184433 91177308-0d34-0410-b5e6-96231b3b80d8
Fix get_magic() handling of short reads.

PR16389


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@184434 91177308-0d34-0410-b5e6-96231b3b80d8