bootstrap problem with trunk on i386-mingw32: target multi-do in libiberty

[FX Coudert]

Bootstrapping today's trunk (rev. 125180) on i386-mingw32 (native)  
leads me to the following error at the end of stage3:

> make[3]: Leaving directory `/home/coudert/ibin/i386-pc-mingw32/ 
> libiberty/testsuite'
> make[3]: Entering directory `/home/coudert/ibin/i386-pc-mingw32/ 
> libiberty'
> make[3]: *** No rule to make target `multi-do'.  Stop.
> make[3]: Leaving directory `/home/coudert/ibin/i386-pc-mingw32/ 
> libiberty'
> make[2]: *** [all] Error 2
> make[2]: Leaving directory `/home/coudert/ibin/i386-pc-mingw32/ 
> libiberty'
> make[1]: *** [all-target-libiberty] Error 2
> make[1]: Leaving directory `/home/coudert/ibin'
> make: *** [all] Error 2

It is true that ${builddir}/i386-pc-mingw32/libiberty/Makefile  
doesn't have a multi-do rule, while the Makefiles for libgfortran and  
libssp do have one. Does someone have an idea how this is triggered?  
What can I post to help people debug this? (I have kept the build  
directory intact for further debugging, I just don't know what to do  
and where to start fishing.)

FX