message: Reformat a comment. NFC.
diff: #if defined(__cplusplus)
  // Include Compiler.h here so we don't define LLVM_FALLTHROUGH and then
  -// Compiler.h
  -// later tries to redefine it.
  +// Compiler.h later tries to redefine it.
  #include "llvm/Support/Compiler.h"
  #ifndef LLVM_FALLTHROUGH
  