maintainer mode parallel make issue

[Eric Blake]

I'm using origin/next at the moment, and seeing failures like this anytime I 
touch configure.ac then attempt a parallel make on cygwin:

$ make -j2 check
CDPATH="${ZSH_VERSION+.}:" && cd . && /bin/sh /home/eblake/m4-patch/build-
aux/missing --run aclocal-1.10c -I ltdl/m4
CDPATH="${ZSH_VERSION+.}:" && cd . && /bin/sh /home/eblake/m4-patch/build-
aux/missing --run autoconf
 cd . && /bin/sh /home/eblake/m4-patch/build-aux/missing --run automake-1.10c --
gnu
/bin/sh ./config.status --recheck
running CONFIG_SHELL=/bin/sh /bin/sh ./configure -C CC=ccache gcc --disable-
shared CFLAGS=-gdwarf-2 -Wall --enable-ltdl-convenience --no-create --no-
recursion
configure: WARNING: unrecognized options: --enable-ltdl-convenience
autom4te: cannot rename autom4te.cache/traces.1t as autom4te.cache/traces.1: No 
such file or directory
automake-1.10c: autoconf failed with exit status: 1
make: *** [Makefile.in] Error 1
make: *** Waiting for unfinished jobs....
configure: loading cache config.cache
...


Both autoconf and automake are stomping on the same autom4te.cache files, and 
when one process completes sooner than the other, the second autom4te process 
loses the battle.  Is this a bug in autom4te for not supporting autoconf and 
automake in parallel, or is it a bug in automake for not serializing these two 
actions when it detects that a change in configure.ac requires rerunning both 
autotools?

-- 
Eric Blake