[doc parsing]: So, in this patch, single character
'commands' will not go through typo fixit logic,
preserving the old behavior (no typo, no diagnostics).
// rdar://12381408


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@181521 91177308-0d34-0410-b5e6-96231b3b80d8