Fix typos in clang

Found via codespell -q 3 -I ../clang-whitelist.txt
Where whitelist consists of:

  archtype
  cas
  classs
  checkk
  compres
  definit
  frome
  iff
  inteval
  ith
  lod
  methode
  nd
  optin
  ot
  pres
  statics
  te
  thru

Patch by luzpaz! (This is a subset of D44188 that applies cleanly with a few
files that have dubious fixes reverted.)

Differential revision: https://reviews.llvm.org/D44188

llvm-svn: 329399
diff --git a/clang/lib/Sema/SemaCast.cpp b/clang/lib/Sema/SemaCast.cpp
index ad63486..f4d8e8d 100644
--- a/clang/lib/Sema/SemaCast.cpp
+++ b/clang/lib/Sema/SemaCast.cpp
@@ -1145,7 +1145,7 @@
       }
     }
   }
-  // Allow arbitray objective-c pointer conversion with static casts.
+  // Allow arbitrary objective-c pointer conversion with static casts.
   if (SrcType->isObjCObjectPointerType() &&
       DestType->isObjCObjectPointerType()) {
     Kind = CK_BitCast;