Add 'setcap' target for sbbs-linux builds to automatically run setcap on

the generated 'sbbs' executable to enable low-port-binding capability.
e.g. run 'make RELEASE=1 setcap symlinks' to make a release (non-debug)
build, set the bind-capability on sbbs, and create symlinks from your
exec directory to the build output (*.exe.release) directory.

src/sbbs3/targets.mk

@@ -101,6 +101,12 @@ symlinks: all
 	ln -sfr umonitor/$(EXEODIR)/* $(SBBSEXEC)
 endif
 
+ifeq ($(os),linux)
+.PHONY: setcap
+setcap: all
+	sudo setcap 'cap_net_bind_service=+ep' $(EXEODIR)/sbbs
+endif
+
 .PHONY: sexyz
 sexyz:	$(SEXYZ)