6810672: Comment typos

I have collected some typos I have found while looking at the code.

Reviewed-by: kvn, never

hotspot/src/share/vm/code/nmethod.cpp

@@ -380,7 +380,7 @@ address nmethod::handler_for_exception_and_pc(Handle exception, address pc) {
 void nmethod::add_handler_for_exception_and_pc(Handle exception, address pc, address handler) {
   // There are potential race conditions during exception cache updates, so we
   // must own the ExceptionCache_lock before doing ANY modifications. Because
-  // we dont lock during reads, it is possible to have several threads attempt
+  // we don't lock during reads, it is possible to have several threads attempt
   // to update the cache with the same data. We need to check for already inserted
   // copies of the current data before adding it.
 

hotspot/src/share/vm/code/nmethod.hpp

@@ -167,7 +167,7 @@ class nmethod : public CodeBlob {
   nmFlags flags;           // various flags to keep track of nmethod state
   bool _markedForDeoptimization;       // Used for stack deoptimization
   enum { alive        = 0,
-         not_entrant  = 1, // uncommon trap has happend but activations may still exist
+         not_entrant  = 1, // uncommon trap has happened but activations may still exist
          zombie       = 2,
          unloaded     = 3 };