[committed] Adding missing prototype for __clzhi2 to xstormy port

xstormy16 has failed since the c99 transition due to a missing prototype for
__clzhi2 in the implementation of stormy16_count_leading_zeros.

This fixes the missing prototype.  Pushed to the trunk.

include/
	* longlong.h (__stormy16_count_leading_zeros): Add prototype for
	__clzhi2.