[gdb/testsuite] Add missing ranges base in dw2-objfile-overlap-*.S

When doing a gdb testsuite run with this trigger patch:
...
@@ -14454,6 +14454,7 @@ dwarf2_ranges_process

       if (!base.has_value ())
        {
+         gdb_assert (false);
          /* We have no valid base address for the ranges
             data.  */
          complaint (_("Invalid .debug_ranges data (no base address)"));
...
we run into the assert with test-case gdb.dwarf2/dw2-objfile-overlap.exp.

Fix this by adding the missing .debug_ranges base in
gdb.dwarf2/dw2-objfile-overlap-*.S.

Tested on x86_64-linux.

gdb/testsuite/ChangeLog:

2020-10-26  Tom de Vries  <tdevries@suse.de>

	* gdb.dwarf2/dw2-objfile-overlap-inner.S: Specify default base address
	for CU.
	* gdb.dwarf2/dw2-objfile-overlap-outer.S: Same.