- (dtucker) [defines.h] Add va_copy if we don't already have it, taken from
   openbsd-compat/bsd-asprintf.c.
 - (dtucker) [regress/unittests/sshbuf/*.c regress/unittests/test_helper/*]
   Wrap stdlib.h include an ifdef for platforms that don't have it.
 - (tim) [regress/unittests/test_helper/test_helper.h] Add includes.h for
   u_intXX_t types.