mingw32 subtle build failure

[FX Coudert <fxcoudert at gmail dot com>]

Hi all, hi mingw32 maintainers,

I'm experiencing a strange bug building mainline as a native compiler  
on i386-pc-mingw32 (with MSYS). It builds fine with the following  
configure line:

> ../gcc/configure   --prefix=/mingw --with-gmp=/home/coudert/local -- 
> disable-nls --with-ld=/mingw/bin/ld --with-as=/mingw/bin/as -- 
> disable-werror --enable-bootstrap --enable-threads --host=i386-pc- 
> mingw32 --enable-languages=c,fortran

If I add the --enable-libgomp option (I know libgomp is not supposed  
to compile, but go on reading) it fails in configure-stage3- 
libdecnumber (that is, even *before* doing anything with libgomp):  
the error (from config.log) is the following:

> configure:1751: error: C compiler cannot create executables
> xgcc.exe: CreateProcess: No such file or directory

Now, if I run the same command line that failed during configure,  
directly inside a shell, it works nicely. To understand this strange  
failure, I changed libiberty/pex-win32.c to print

> printf ("CreateProcess (%s, %s, ...)\n", full_executable, cmdline);

just before the CreateProcess call, I get the following output:

> configure:1706: checking for C compiler default output file name
> configure:1709:  /home/coudert/ibin-openmp/./prev-gcc/xgcc -B/home/ 
> coudert/ibin-
> openmp/./prev-gcc/ -B/mingw/i386-pc-mingw32/bin/ -g -O2    
> conftest.c  >&5
> CreateProcess (C:\msys\1.0.10\home\coudert\ibin-openmp\prev-gcc 
> \cc1.exe, "C:/msy
> s/1.0.10/home/coudert/ibin-openmp/prev-gcc/cc1.exe" "-quiet" "- 
> iprefix" "c:\msys
> \1.0.10\home\coudert\ibin-openmp\prev-gcc\../lib/gcc/i386-pc- 
> mingw32/4.2.0/" "-i
> system" "C:/msys/1.0.10/home/coudert/ibin-openmp/prev-gcc/include"  
> "conftest.c"
> "-quiet" "-dumpbase" "conftest.c" "-mtune=i386" "-auxbase"  
> "conftest" "-g" "-O2"
> "-o" "C:/DOCUME~1/coudert/LOCALS~1/Temp/ccIVaaaa.s", ...)^M
> CreateProcess (C:\msys\1.0.10\home\coudert\ibin-openmp\prev-gcc\as,  
> "C:/msys/1.0
> .10/home/coudert/ibin-openmp/prev-gcc/as" "-o" "C:/DOCUME~1/coudert/ 
> LOCALS~1/Tem
> p/ccgHbaaa.o" "C:/DOCUME~1/coudert/LOCALS~1/Temp/ccIVaaaa.s", ...)^M
> CreateProcess (C:\msys\1.0.10\bin\sh.exe, "\bin\sh" "C:/msys/1.0.10/ 
> home/coudert
> /ibin-openmp/prev-gcc/as" "-o" "C:/DOCUME~1/coudert/LOCALS~1/Temp/ 
> ccgHbaaa.o" "C
> :/DOCUME~1/coudert/LOCALS~1/Temp/ccIVaaaa.s", ...)^M
> xgcc.exe: CreateProcess: No such file or directory^M

I'm trying to understand exactly why all this only happens for -- 
enable-libgomp builds (it's 100% reproducible for me, with different  
versions of mainline, bootstrapping everytime). So, is what I'm  
seeing an expected behaviour? How can I investigate further?

Thanks,
FX