Recent MinGW postgres builds with -O2 do not pass regression tests

When building a minimal PostgreSQL under the latest mingw (20111118),
make check will give a few dozen fails with the server exiting on code
2. The build is fine when -O2 is removed from the CFLAGS. This behaviour
is present on all revs on the REL9_1_STABLE branch that I tested, among
which were 9.1.3 and 9.1.0.

$ gcc -v
Using built-in specs.
COLLECT_GCC=C:\MinGW\bin\gcc.exe
COLLECT_LTO_WRAPPER=c:/mingw/bin/../libexec/gcc/mingw32/4.6.1/lto-wrapper.exe
Target: mingw32
Configured with: ../gcc-4.6.1/configure
--enable-languages=c,c++,fortran,objc,ob
j-c++ --disable-sjlj-exceptions --with-dwarf2 --enable-shared
--enable-libgomp -
-disable-win32-registry --enable-libstdcxx-debug
--enable-version-specific-runti
me-libs --build=mingw32 --prefix=/mingw
Thread model: win32
gcc version 4.6.1 (GCC)

regards,
Yeb