re PR fortran/54426 (FAIL: gfortran.dg/common_6.f90  -O  (internal compiler error) on powerpc-apple-darwin9)

2012-09-02  Tobias Burnus  <burnus@net-b.de>

        PR fortran/54426
        * symbol.c (find_common_symtree): New function.
        (gfc_undo_symbols): Use it; free common_head if needed.

From-SVN: r190853