Work around InterlockedExchange not exported from kernel32.dll on x64

...as reported in a comment on <http://msdn.microsoft.com/en-us/library/windows/
desktop/ms683590%28v=vs.85%29.aspx> "InterlockedExchange function"

Change-Id: Ie71edd7a5ce8ff3c922d607e174a4c4d43c08c1d

external/nss/nss.windows.patch

@@ -20,3 +20,14 @@
  
  $(OBJDIR)/$(PROG_PREFIX)%$(OBJ_SUFFIX): %.c
  	@$(MAKE_OBJDIR)
+--- a/a/nspr/pr/include/md/_win95.h
++++ b/b/nspr/pr/include/md/_win95.h
+@@ -312,7 +312,7 @@
+ #define _MD_ATOMIC_ADD(ptr,val)    (InterlockedExchangeAdd((PLONG)ptr, (LONG)val) + val)
+ #define _MD_ATOMIC_DECREMENT(x)       InterlockedDecrement((PLONG)x)
+ #endif /* x86 */
+-#define _MD_ATOMIC_SET(x,y)           InterlockedExchange((PLONG)x, (LONG)y)
++#define _MD_ATOMIC_SET(x,y)           _InterlockedExchange((PLONG)x, (LONG)y)
+ 
+ #define _MD_INIT_IO                   _PR_MD_INIT_IO
+