`Makefile' is removed upon interrupt

[Jim Meyering]

I interrupted a build and saw this:
  ...
  Making all in cp
  make[3]: Entering directory `/fetish/cu/tests/cp'
  cd ../.. && \
    /bin/sh /fetish/cu/config/missing --run automake-1.7 --gnits  
tests/cp/Makefile
  cd ../.. && /bin/sh ./config.status tests/cp/Makefile
  config.status: creating tests/cp/Makefile
  make[3]: *** [Makefile] Error 1
  make[2]: *** [all-recursive] Interrupt
  make[1]: *** [all-recursive] Interrupt
  make: *** [all] Interrupt

  [Exit 130 (SIGINT)]

and was surprised when a subsequent `make' command failed
because tests/cp/Makefile had been removed.

Here's how I think that happened:
This is the rule from coreutils/tests/cp/Makefile:

Makefile:  $(srcdir)/Makefile.in  $(top_builddir)/config.status
        cd $(top_builddir) && $(SHELL) ./config.status $(subdir)/$@ 
$(am__depfiles_maybe)

And this looks like the relevant part of config.status:

          sed -e ... -e ... "$ac_dir/Makefile.in" > "$ac_dir/Makefile"

The problem arose because GNU Make removes any target that is
being built when `make' is interrupted.

One way to fix it is to tell GNU make that `Makefile' should not
be removed in such a case, e.g. by adding a line like this:

.PRECIOUS: Makefile

Of course, then we'd also have to ensure that config.status creates Makefile
atomically (redirect to a temp. file and rename when done writing).

If you like that, I'll propose a patch.

Most people don't know to rerun ./config.status to regenerate such a
lost Makefile -- and they shouldn't need to know it.

This is with autoconf-2.57f and automake-1.7.7.