[gdb/symtab] Apply workaround for PR gas/31115 a bit more

[gdb/symtab] Apply workaround for PR gas/31115 a bit more

In commit 8a61ee551ce ("[gdb/symtab] Workaround PR gas/31115"), I applied a
workaround for PR gas/31115 in read_func_scope, fixing test-case
gdb.arch/pr25124.exp.

Recently I noticed that the test-case is failing again.

Fix this by factoring out the workaround into a new function fixup_low_high_pc
and applying it in dwarf2_die_base_address.

While we're at it, do the same in dwarf2_record_block_ranges.

Tested on arm-linux with target boards unix/-marm and unix/-mthumb.

Reviewed-By: Alexandra Petlanova Hajkova <ahajkova@redhat.com>