PR fortran/23057
* dwarf2out.c (gen_variable_die): Represent Fortran COMMON vars
as DW_TAG_variable children of DW_TAG_common_block rather than
DW_TAG_member children. Put DW_AT_external to individual
DW_TAG_variable DIEs, not to DW_TAG_common_block.
* gfortran.dg/debug/pr35154-dwarf2.f: Adjust for replacement
of DW_TAG_member with DW_TAG_variable.