SYSTEM-SPECIFIC HINTS
+for NetBSD:
+ NetBSD 2.0 and above are required because of the lack of needed
+ signal APIs in NetBSD 1.6 and earlier.
+
for OpenBSD:
OpenBSD 3.0 has stricter ulimit values, and/or enforces them more
strictly, than its predecessors. Therefore SBCL's initial mmap()