[gdb/testsuite] Fix overlapping CUs in gdb.dwarf2/dw2-entry-points.exp

[gdb/testsuite] Fix overlapping CUs in gdb.dwarf2/dw2-entry-points.exp

When running test-case gdb.dwarf2/dw2-entry-points.exp with target board
cc-with-gdb-index, I get:
...
(gdb) file dw2-entry-points^M
Reading symbols from dw2-entry-points...^M
warning: .gdb_index address table has a range (0x40066c - 0x4006e4) that \
  overlaps with an earlier range, ignoring .gdb_index^M
(gdb) delete breakpoints^M
...

Fix this by copying function bar_helper to barso_helper, and using it where
appropriate.

Tested on aarch64-linux.

Approved-By: Tom Tromey <tom@tromey.com>
PR testsuite/33315
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=33315