[3.6] bpo-30983: [gdb] Fix py-bt, etc. for non-debug shared builds (GH-3153) (#3192)

[3.6] bpo-30983: [gdb] Fix py-bt, etc. for non-debug shared builds (GH-3153) (#3192)

PEP 523 introduced _PyEval_EvalFrameDefault which inlines PyEval_EvalFrameEx on
non-debug shared builds.  This breaks the ability to use py-bt, py-up, and
a few other Python-specific gdb integrations.

This patch fixes the problem by only looking for _PyEval_EvalFrameDefault
frames.

test_gdb passes on both a debug and a non-debug build.

Original patch by Bruno "Polaco" Penteado.
(cherry picked from commit 5fe59f8e3a0a56a155c18f9d581205ec533764b6)