[gdb/testsuite] Use compiler-generated instead of gas-generated stabs

[gdb/testsuite] Use compiler-generated instead of gas-generated stabs

The test-case gdb.dwarf2/dw2-ranges.exp is the only one in the gdb testsuite
that uses gas-generated stabs.

While the use seems natural alongside the use of gas-generated dwarf in the
same test-case, there are a few known issues, filed on the gdb side as:
- PR symtab/12497 - "stabs: PIE relocation does not work"
- PR symtab/28221 - "[readnow, stabs] FAIL: gdb.dwarf2/dw2-ranges.exp: \
  info line func"
and on the gas side as:
- PR gas/28233 - "[gas, --gstabs] Generate stabs more similar to gcc"

The test-case contains a KFAIL for PR12497, but it's outdated and fails to
trigger.

The intention of the test-case is to test gas-generated dwarf, and using
gcc-generated stabs instead of gas-generated stabs works fine.

Supporting compiler-generated stabs is already a corner-case for gdb, and
there's no current commitment/incentive to support/workaround gas-generated
stabs, which can be considered a corner-case of a corner-case.

Work around these problem by using compiler-generated stabs in the test-case.

Tested on x86_64-linux.

gdb/testsuite/ChangeLog:

2021-08-22  Tom de Vries  <tdevries@suse.de>

	* gdb.dwarf2/dw2-ranges.exp: Use compiler-generated stabs.