Changed OS_ARCH to OS_TARGET for NTO because we are still cross-compiling.

Thanks to Jerry L. Kirk <Jerry.Kirk@Nexwarecorp.com> for the patch.
(This might have been my error when I checked in his previous patch.)

nsprpub/pr/include/md/Makefile

@@ -139,7 +139,7 @@ ifeq ($(OS_ARCH),QNX)
 MDCPUCFG_H = _qnx.cfg
 endif
 
-ifeq ($(OS_ARCH),NTO)
+ifeq ($(OS_TARGET),NTO)
 MDCPUCFG_H = _nto.cfg
 endif