sys/_bitset.h: revert commit 74e014dbfab

It caused kernel build for PowerPC64 to fail.

A different patch is being tested with make universe to make sure it
works on all architectures.

MFC after:	1 month<N [day[s]|week[s]|month[s]].  Request a reminder email>

newlib/libc/sys/rtems/include/sys/_bitset.h

@@ -61,13 +61,11 @@ struct _t {								\
  * Define a default type that can be used while manually specifying size
  * to every call.
  */
-__BITSET_DEFINE(__bitset, 1);
+__BITSET_DEFINE(bitset, 1);
 
 #if defined(_KERNEL) || defined(_WANT_FREEBSD_BITSET)
 #define	BITSET_DEFINE(_t, _s)	__BITSET_DEFINE(_t, _s)
 #define	BITSET_DEFINE_VAR(_t)	__BITSET_DEFINE_VAR(_t)
-
-#define	bitset			__bitset
 #endif
 
 #endif /* !_SYS__BITSET_H_ */