Improve robustness of 'make bootstrap'.

Run autogen.sh after bootstrap-clean, to avoid bzr pull issues.
* INSTALL, README: Document autogen.sh.
* Makefile.in (Makefile): Mark it as precious, since it's updated
atomically.
(MAKE_CONFIG_STATUS): New macro.
(config.status, bootstrap): Use it.  This causes 'make bootstrap'
to run config.status with the --recheck option, which is more
appropriate for a bootstrap.
(bootstrap): Run autogen.sh right after cleaning.  Don't worry
about failures due to missing tools.
* autogen.sh: Exit with status 101 when failing due to missing tools.
* make-dist: Distribute autogen.sh.

Fixes: debbugs:12376

1 files changed, 8 insertions, 3 deletions

diff --git a/README b/README
index a11935ee3e8..2c50c5bbb91 100644
--- a/README
+++ b/README
@@ -41,9 +41,14 @@ The file `configure.ac' is the input used by the autoconf program to
 construct the `configure' script.  Since Emacs has some configuration
 requirements that autoconf can't meet directly, and for historical
 reasons, `configure.ac' uses an unholy marriage of custom-baked
-configuration code and autoconf macros.  If you want to rebuild
-`configure' from `configure.ac', you will need to install a recent
-version of autoconf and GNU m4.
+configuration code and autoconf macros.
+
+The shell script `autogen.sh' generates 'configure' and other files by
+running the GNU build tools autoconf and automake, which in turn use
+GNU m4 and Perl.  If you want to use it, you will need to install
+recent versions of these build tools.  This should be needed only if
+you edit files like `configure.ac' that specify Emacs's autobuild
+procedure.
 
 The file `Makefile.in' is a template used by `configure' to create
 `Makefile'.