Fix known typos

Sweep the codebase for common typos. Includes some changes to visible function
names that were misspelt.

llvm-svn: 200018
diff --git a/llvm/lib/Support/APFloat.cpp b/llvm/lib/Support/APFloat.cpp
index 802233c..deb9b05 100644
--- a/llvm/lib/Support/APFloat.cpp
+++ b/llvm/lib/Support/APFloat.cpp
@@ -3776,7 +3776,7 @@
     //                     change the payload.
     if (isSignaling()) {
       result = opInvalidOp;
-      // For consistency, propogate the sign of the sNaN to the qNaN.
+      // For consistency, propagate the sign of the sNaN to the qNaN.
       makeNaN(false, isNegative(), 0);
     }
     break;