Don't use dwfl_module bias in either emit_address() and vardie_from_symtable().

Don't use dwfl_module bias in either emit_address() and vardie_from_symtable().

dwflpp::emit_address() is called by loc2c for emitting DW_OP_addr.
DW_OP_addr could come from the actual dwarf location description or
could be synthetically generated from through vardie_from_symtable().
vardie_from_symtable() would keep the dwfl module bias (if there was one),
but the DW_OP_addr from real dwarf debuginfo would not have it.
Now we are consistently not having the module bias added.

Add some variants of the externalvar.exp testcase, which previously
failed with older GCC versions (where we would pick up the DW_OP_addr
from the dwarf location description), while newer GCCs emit dwarf DIEs
for these variables that only have the external flag set. The new
testcase variants use static vars, which will have DW_OP_addr emitted
in both old and new GCC versions.