[Makefile] Use .PRECIOUS instead of .SECONDARY for bin/%.tmp targets

Revert "Use .SECONDARY instead of .PRECIOUS for bin/%.tmp targets."

This reverts commit de29e5a39c.

.SECONDARY doesn't seem to work properly with the target patterns of
implicit rules.  In particular, a "make clean ; make bin/rtl8139.dsk"
will correctly leave the bin/rtl8139.dsk.tmp file present when .PRECIOUS
is used, but not when .SECONDARY is used.

This is slightly irritating since we don't want the
"do-not-delete-if-interrupted" semantics of .PRECIOUS, but it seems to be
the best compromise.

src/Makefile.housekeeping

 	$(Q)$(OBJDUMP) -ht $@ | $(SORTOBJDUMP) >> $(BIN)/$*.tmp.map
 
 # Keep intermediate object file (useful for debugging)
-.SECONDARY : $(BIN)/%.tmp
+.PRECIOUS : $(BIN)/%.tmp
 
 # Show a linker map for the specified target
 #