rpcgen will error out if the file it's asked to create already exists.
Several other rules in sunrpc/Makefile take care to delete rpcgen-
generated files before creating them, but rpcgen-tests doesn't, which
can lead to spurious test failures in an incremental rebuild.
* sunrpc/Makefile (rpcgen-tests): Delete the .out file before
creating or re-creating it.
ifeq ($(run-built-tests),yes)
$(rpcgen-tests): $(objpfx)%.out: %.x $(objpfx)rpcgen
+ -rm -f $@
$(built-program-cmd) -c $< -o $@; \
$(evaluate-test)
endif