bisect-runner.pl needs another minor fixup to build 5.004_05 on Linux.

bisect-runner.pl needs another minor fixup to build 5.004_05 on Linux.

bisect-runner.pl already reverts a sequence of commits to doio.c related to
special case handling of union semun on Linux and Solaris, which cause the
build to fail on current Linux. The last of these, 9b599b2a63d2324d is
described as "[win32] merge change#887 from maintbranch". However, it uses
__sun__ and __svr4__ instead of the __sun and __SVR4 of the maint branch
commit 6cdf74fe31f049dc. Hence the code in bisect-runner.pl needs to be
taught about this variation in the maint-5.004 branch, so that it can also
unwind the problematic code in doio.c there.