[gdb] Ignore .sframe section in dtrace_static_probe_ops::get_probes

On aarch64-linux (Debian testing), with test-case gdb.base/fission-macro.exp I
run into:
...
(gdb) set complaints 5^M
(gdb) file fission-macro-v4-b32-s0^M
Reading symbols from fission-macro-v4-b32-s0...^M
During symbol reading: \
  skipping section '.sframe' which does not contain valid DOF data.^M
(gdb) FAIL: $exp: lang=c: dwarf_version=4: dwarf_bits=32: strict_dwarf=0: \
  No complaints
...

The problem is that there's an overlap between:
...
./include/elf/common.h:#define SHT_SUNW_dof                 0x6ffffff4
...
and:
...
./include/elf/common.h:#define SHT_GNU_SFRAME		     0x6ffffff4
...

So when dtrace_static_probe_ops::get_probes tries reading an SHT_SUNW_dof
section, it fails to read the corresponding magic number and bails with this
complaint:
...
During symbol reading: \
  skipping section '.sframe' which does not contain valid DOF data.^M
...

But the section actually being read is not an SHT_SUNW_dof section, but an
SHT_GNU_SFRAME section:
...
[Nr] Name      Type            Address          Off    Size   ES Flg Lk Inf Al
[17] .sframe   GNU_SFRAME      00000000000008f0 0008f0 000035 00   A  0   0  8
...

Fix this by checking for the section name .sframe in
dtrace_static_probe_ops::get_probes.

Tested on aarch64-linux.

Approved-By: Simon Marchi <simon.marchi@efficios.com>

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=33813