Add the change to a spinlock in the change log

changelog.dd

@@ -9,6 +9,10 @@ $(LI $(RELATIVE_LINK2 aa-clear, A `clear` method has been added to associative
     arrays to remove all elements.))
 )
 
+$(LI $(RELATIVE_LINK2 spinlock, The GC now uses a spinlock instead of a
+recursive mutex.))
+)
+
 $(BUGSTITLE Library Changes,
 
 $(LI $(LNAME2 aa-clear, A `clear` method has been added to associative
@@ -27,6 +31,14 @@ aa.clear(); // still retains its current capacity for faster imports
 assert(aa2.length == 0); // other references affected
 -------
 )
+
+$(LI $(LNAME2 spinlock, The GC is no longer wrapped in a pthread_mutex, it
+    now uses a spinlock.)
+
+    $(P This results in a 5% faster GC on average, with the most benefits going
+        to multi-threaded programs that use the GC. See $(DRUNTIMEPR 1447) for
+        more details.
+    )
 )
 
 
@@ -43,5 +55,8 @@ Macros:
     XREF = <a href="phobos/std_$1.html#$2">$2</a>
     CXREF = <a href="phobos/core_$1.html#$2">$2</a>
 
+    PULL_REQUEST = $(LINK2 https://github.com/D-Programming-Language/$1/pull/$2, $1#$2)
+    DRUNTIMEPR = $(PULL_REQUEST druntime,$1)
+
     BOOKTABLE = <table><caption>$1</caption>$+</table>
     PRE = <pre>$0</pre>