Build fails on `aarch64-unknown-linux-android24`.

[ChenPi11]

On aarch64 Termux environment, installing pyppmd via pip (or build from source) fails with:

src/lib/buffer/ThreadDecoder.c:182:9: error: call to undeclared function 'pthread_cancel'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
  182 |         pthread_cancel(tc->handle);
      |         ^
src/lib/buffer/ThreadDecoder.c:182:9: note: did you mean 'pthread_once'?
/data/data/com.termux/files/usr/include/pthread.h:264:5: note: 'pthread_once' declared here
  264 | int pthread_once(pthread_once_t* _Nonnull __once, void (* _Nonnull __init_routine)(void));
      |     ^
src/lib/buffer/ThreadDecoder.c:277:9: error: call to undeclared function 'pthread_cancel'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
  277 |         pthread_cancel(tc->handle);
      |         ^
2 errors generated.
error: command '/data/data/com.termux/files/usr/bin/aarch64-linux-android-clang' failed with exit code 1

ERROR Backend subprocess exited when trying to invoke build_wheel

Termux's pthread.h do not provide a implementation for pthread_cancel. So we cannot build it.

Replace pthread_cancel(tc->handle) to pthread_kill(tc->handle, SIGUSR1) can fix this problem. With all tests passed.
But it seems unsafe.

Environment

OS: Android 13 Termux 0.118.1
Kernel: aarch64 Linux 4.14.186
Version: pyppmd 1.2.1.dev0 (latest)

[miurahr]

When there is no other way to implement, it may be a solution even it is unsfe.
You are welcome to give a pull-request to change it only when aarch64-unknown-linux-android24