* gendef: Add SEH information to sigfe entry points, as well as to
	_sigfe and _sigbe.
	* cygmalloc.h: Include regparm.h rather than defining __reg{1,2,3} here.
	* ptmalloc3.cc (__malloc_initialized): Define as type LONG on Cygwin
	and include windows.h.
	(ptmalloc_init): Set __malloc_initialized on Cygwin using
	InterlockedCompareExchange and carefully check for concurrency
	situation.