bpo-40010: Pass tstate to ceval GIL functions

[vstinner]

• 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

[vstinner]

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

I wrote PR #19080 to fix crashes.

[vstinner]

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

[vstinner]

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\\)
'

[vstinner]

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.