Always check HAVE_FORK==1 if defined

Always check HAVE_FORK==1 if defined

For autotools this is not an issue, as HAVE_FORK is only
defined if fork is available, and thus HAVE_FORK==1.

Cmake, though, will define it either way, so it is possible
for HAVE_FORK==0. Most of these were caught earlier, but
a few were missed.

git-svn-id: svn+ssh://svn.code.sf.net/p/check/code/trunk@997 64e312b2-a51f-0410-8e61-82d0ca0eb02a