DragonFlyBSD/src 3f7c286include spawn.h, sys/sys _sigset.h select.h

Don't include the full <sys/signal.h> in headers that just need sigset_t.

Namely, <select.h> and <spawn.h>.

Split it out into a separate header, <sys/_sigset_t.h> and include that
in <spawn.h> and <sys/select.h>.

This cleans up these two headers' name space considerably.

Thanks to zrj for testing with a dports bulk build.
DeltaFile
+41-0sys/sys/_sigset.h
+10-12sys/sys/select.h
+5-6sys/sys/signal.h
+6-1include/spawn.h
+62-194 files

UnifiedSplitRaw