Add .PHONY targets, to declare targets that aren't real files.

Add .PHONY targets, to declare targets that aren't real files.

Immediate benefit: when you use "make -t" to avoid a global recompile
after a trivial header file touchup, Make will no longer create files
named all, oldsharedmods, and sharedmods.

(Not sure if I tracked down all such targets.  Not sure if I care.)