add mention of INFLATING() to share/oops/markWord.hpp header comment

David H. noticed that the header comment in
src/hotspot/share/oops/markWord.hpp that discusses
the markWord encoding does not mention the
special INFLATING value.

Here's a proposal:

$ hg diff
diff -r 73778bfbffe3 src/hotspot/share/oops/markWord.hpp
--- a/src/hotspot/share/oops/markWord.hpp Thu Aug 13 10:02:35 2020 -0400
+++ b/src/hotspot/share/oops/markWord.hpp Thu Aug 13 10:51:44 2020 -0400
@@ -86,6 +86,10 @@
 // [ptr | 11] marked used to mark an object
 //
 // We assume that stack/thread pointers have the lowest two bits cleared.
+//
+// - INFLATING() is a distinguished markword value that is used when
+// inflating an existing stack lock into an ObjectMonitor. See below
+// for is_being_inflated() and INFLATING().
 
 class BasicLock;
 class ObjectMonitor;
@@ -226,7 +230,7 @@
   bool is_being_inflated() const { return (value() == 0); }
 
   // Distinguished markword value - used when inflating over
- // an existing stacklock. 0 indicates the markword is "BUSY".
+ // an existing stack lock. 0 indicates the markword is "BUSY".
   // Lockword mutators that use a LD...CAS idiom should always
   // check for and avoid overwriting a 0 value installed by some
   // other thread. (They should spin or block instead. The 0 value