Fix spelling mistakes in Transforms comments. NFC.

Identified by Pedro Giffuni in PR27636.

llvm-svn: 287488
diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index 028ae14..ad6e0c1 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -2576,7 +2576,7 @@
           // remove it from the filter.  An unexpected type handler may be
           // set up for a call site which throws an exception of the same
           // type caught.  In order for the exception thrown by the unexpected
-          // handler to propogate correctly, the filter must be correctly
+          // handler to propagate correctly, the filter must be correctly
           // described for the call site.
           //
           // Example: