Some of our targets use "bison --help", but they can't depend on
"bison" itself (to avoid additional requirements on the user), so
they used to call "make src/bison" in the commands. Then
concurrent builds may fail: one make might be aiming one of its
jobs at compiling src/bison, and another job at generating the man
page. If the latter is faster than the former, then we have two
makes that concurrently try to compile src/bison.
This might also be a more convincing explanation for the failure
described in the patch "build: fix paths".
* Makefile.am (SUFFIXES): Initialize.
* build-aux/move-if-change: New, symlink to gnulib's.
* build-aux/local.mk: Ship it.
* doc/common.x: Remove, merged into...
* doc/bison.x: here.
* doc/local.mk (doc/bison.help): New.
($(CROSS_OPTIONS_TEXI)): Depend on it.
Use src/bison.
(.x.1): Replace with...
(doc/bison.1): this explicit, simpler, target.
(common_dep): Remove, inlined where appropriate.
(SUFFIXES, PREPATH): Remove, unused.
* doc/common.x, doc/bison.x: New.
* doc/Makefile.am (bison.1, .x.1): New.
The code is taken from autoconf-2.61/man/Makefile.am.
* configure.ac: Look for help2man.
