Changes

GHA: update from checkout@v4 to checkout@v5

GHA: update Debian i386 image

GHA: factor Android NDK et API level numbers

GHA: fold config.log output in failed cross-builds

Turn off the echo'ing of command with `set +x` when displaying
`config.log`, otherwise it may scramble the output.

No `pthread_cancel` in Android's Bionic libc

Replacing `pthread_cancel` with assert using the preprocessor doesn't
work if `assert` isn't defined either! It was `<assert.h>` that was
missing, prefer detecting at configure-time whether `pthread_cancel`
is supported, and guard its use. Another option would be to guard its
use using the `__BIONIC__` macro.

- https://android.googlesource.com/platform/bionic/+/master/tests/headers/posix/pthread_h.c#90
- https://stackoverflow.com/questions/26823926/pthread-cancel-not-found-compiling-with-android-toolchain

Misc. Autoconf simplifications