> Do you know in which precise test it hangs?

They are named in the first msg of each issue, the issues are:
    issue #26938: android: test_concurrent_futures hangs on armv7
    issue #26939: android: test_functools hangs on armv7
    issue #26940: android: test_importlib hangs on armv7
    issue #26941: android: test_threading hangs on armv7

The test_threading and test_importlib issues have also now a gdb backtrace, so we know not only the test name but also the full python frame stack with line numbers thanks to python-gdb.py magic. It seems that test_functools, test_threading and test_importlib all hang within take_gil().

test_concurrent_futures is different and hangs in a futex().

With "thread apply all backtrace",  nothing changes and gdb still prints:
    Cannot access memory at address 0x0
    #0  0xb6efae6c in ?? ()
    #1  0xb6efd830 in ?? ()
    Backtrace stopped: previous frame identical to this frame (corrupt stack?)

The problem seems to be that gdb does not have enough information to unwind the stack for the other threads and for thread #1 it only works after an interrupted continue command, and not on gdb startup.