bpo-40010: Pass tstate to ceval GIL functions

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• Add eval_frame_handle_pending() helper function: cold code path.
• Fix PyEval_ReleaseLock(): don't dereference tstate if it's NULL.

https://bugs.python.org/issue40010

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Hum, https://bugs.python.org/issue39877 strikes back. One more time.

I wrote PR #19080 to fix crashes.

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I merged PR #19080. I rebased this PR on top of it.

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Oh, test_gdb failed on Travis CI beause gdb fails to get some Python frames: (frame information optimized out). Example of error:

AssertionError: 'Breakpoint 1 at 0x5aabf1: file Python/bltinmodule.c, line 1173.
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".

Breakpoint 1, builtin_id (self=, v=42) at Python/bltinmodule.c:1173
1173\t    PyObject *id = PyLong_FromVoidPtr(v);
Traceback (most recent call first):
  <built-in method id of module object at remote 0x7ffff7f87050>
  (frame information optimized out)
  File "/home/travis/build/python/cpython/Lib/test/gdb_sample.py", line 7, in bar
    baz(a, b, c)
  File "/home/travis/build/python/cpython/Lib/test/gdb_sample.py", line 4, in foo
    bar(a, b, c)
  (frame information optimized out)
'

did not match 

'^.*
Traceback \\(most recent call first\\):
  <built-in method id of module object .*>
  File ".*gdb_sample.py", line 10, in baz
    id\\(42\\)
  File ".*gdb_sample.py", line 7, in bar
    baz\\(a, b, c\\)
  File ".*gdb_sample.py", line 4, in foo
    bar\\(a, b, c\\)
  File ".*gdb_sample.py", line 12, in <module>
    foo\\(1, 2, 3\\)
'

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Oh, test_gdb failed on Travis CI beause gdb fails to get some Python frames: (frame information optimized out).

I created https://bugs.python.org/issue40019 to fix this issue.

I added PR #19081 commit to this PR to test if PR #19081 fix https://bugs.python.org/issue40019.