The tool builds all releases travelling back from the current one up
to the named one. For example:

  ./tools/git-compileall master

  [... all the compiles ...]

   Number of failed builds: 0
   The log of all compiles is at /tmp/makeall.out.67Rf3n
   The md5sums of wrc.o are at /tmp/mdlog.sZXrAi

The tool was born for internal use, so it is misnamed and so on. But
it may be useful to others too.
Signed-off-by: Alessandro Rubini <rubini@gnudd.com>