ICE on bootstrap of libstdc++ for mingw-targets in add_bb_to_loop

[Kai Tietz]

Hello,

recent changes to cfgloop have caused an ICE on bootstrapping
libstdc++ for mingw targets.  I assume same ICE happens for cygwin
hosted gcc bootstrap, too. ICE happens on compiling of
gcc/libstdc++-v3/libsupc++/eh_alloc.cc

Code which produces seg-fault is in macro:

      DEF_VEC_P (loop_p);

backtrace:

#0  add_bb_to_loop (bb=0x7ef68ca0, loop=0x0) at ../../gcc/gcc/cfgloop.h:88
#1  0x00a5e3d7 in split_block (bb=0x7ef68bc8, i=0x7eb6ea30)
    at ../../gcc/gcc/cfghooks.c:450
#2  0x00abaf49 in find_many_sub_basic_blocks (blocks=0x442f178)
    at ../../gcc/gcc/cfgbuild.c:474
#3  0x008a280f in break_superblocks () at ../../gcc/gcc/cfglayout.c:1345
#4  0x007293f9 in finish_eh_generation () at ../../gcc/gcc/except.c:1431
#5  0x00dc06f4 in gimple_expand_cfg () at ../../gcc/gcc/cfgexpand.c:4652
#6  0x008d4afc in execute_one_pass (pass=0x1143bc0)
    at ../../gcc/gcc/passes.c:2079
#7  0x008d4cc4 in execute_pass_list (pass=0x4350238)
    at ../../gcc/gcc/passes.c:2134
#8  0x00a8b1c4 in tree_rest_of_compilation (fndecl=0x7eca1d00)
    at ../../gcc/gcc/tree-optimize.c:422
#9  0x008da273 in cgraph_expand_function (node=0x7ecd7578)
    at ../../gcc/gcc/cgraphunit.c:1784
#10 0x008dc2d9 in cgraph_optimize () at ../../gcc/gcc/cgraphunit.c:1851
#11 0x008dcb2e in cgraph_finalize_compilation_unit ()
    at ../../gcc/gcc/cgraphunit.c:2628
#12 0x00510c5b in cp_write_global_declarations ()
    at ../../gcc/gcc/cp/decl2.c:4077
#13 0x008e6452 in toplev_main (argc=30, argv=0x43497d0)
    at ../../gcc/gcc/toplev.c:572
#14 0x006a104a in main (argc=30, argv=0x43497d0) at ../../gcc/gcc/main.c:36