libffi crashes libgobject when compiled without optimizations

[LRN <lrn1986 at gmail dot com>]

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I'm using mingw.org i386 gcc 4.7.2
When i compile libffi with -O1, everything works fine.
If i replace "-O1" with " -O0 \
 -fauto-inc-dec \
 -fcompare-elim  \
 -fcprop-registers  \
 -fdce  \
 -fdefer-pop  \
 -fdelayed-branch  \
 -fdse  \
 -fguess-branch-probability  \
 -fif-conversion2  \
 -fif-conversion  \
 -fipa-pure-const  \
 -fipa-profile  \
 -fipa-reference  \
 -fmerge-constants \
 -fsplit-wide-types  \
 -ftree-bit-ccp  \
 -ftree-builtin-call-dce  \
 -ftree-ccp  \
 -ftree-ch  \
 -ftree-copyrename  \
 -ftree-dce  \
 -ftree-dominator-opts  \
 -ftree-dse  \
 -ftree-forwprop  \
 -ftree-fre  \
 -ftree-phiprop  \
 -ftree-sra  \
 -ftree-pta  \
 -ftree-ter \
 -funit-at-a-time \
 -fomit-frame-pointer \
"
(that is, -O0 and all the optimizations that -O1 enables)
libffi crashes when libgobject is unloaded.

The crash can be reproduced with this program:

#include <windows.h>
#include <stdio.h>

int
main (int argc, char **argv)
{
  HMODULE h;

  h = LoadLibraryA ("libgobject-2.0-0.dll");
  if (h == NULL)
    printf ("Failed to loadlib: %lu\n", GetLastError ());
  else
    FreeLibrary (h);
  return 0;
}

The version of glib doesn't matter much (anything released within last
couple of years will do, i think). The version of libffi doesn't
matter either (verified for the first commit after 3.0.10 (i.e. the
one that bumped the interface)).
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