Termux compilation tips

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I needed it for pytorch compilation. Spent half a day trying to compile this, as dependency. Tips for Termux users only:
1. If you're compiling this code on Termux and encounter an error about the missing 'unistd.h' file, you might need to install the 'ndk-sysroot'. It has it natively, one of very few apt packages that does not get installed to /opt or .local/lib
2. Remove this code security cruft first, as it gets stuck eith smth Google. Yes. Thus :
```
alias cmakeinstall='rm CMakeCache.txt && echo "Removing silly Werror 🪲 directives en masse..." & time find . -type f -exec sed -i "s/-Werror//g" {} \; && export CFLAGS="-fuse-ld=lld -pthread -g -march=armv8-a -mtune=cortex-a53 -Wall -Wextra" && echo "Starting compilation 👩‍💻 proper... "&& cmake -DCMAKE_INSTALL_PREFIX=$PREFIX . && time make -j4 && make install'
```
is my newest one liner.

Ref:
```
~/downloads/pthreadpool $ uname -a Linux localhost 4.14.186+ #1 SMP PREEMPT Thu Mar 17 16:28:22 CST 2022 aarch64 Android ~/downloads/pthreadpool $
```

PS. You may test it with:
```
#include #include void task(void* arg, size_t i) { printf("Hello from task %zu\n", i); } int main() { pthreadpool_t pool = pthreadpool_create(4); pthreadpool_parallelize_1d(pool, (pthreadpool_task_1d_t)task, NULL, 10, 0); pthreadpool_destroy(pool); return 0; }
```
with : `gcc -o test4 test4.c -pthread -lpthreadpool` :
~/.../pytorch/build $ ./test4 Hello from task 3 Hello from task 4 Hello from task 5 Hello from task 2 Hello from task 1 Hello from task 9 Hello from task 7 Hello from task 0 Hello from task 6 Hello from task 8 ~/.../pytorch/build $

...

No documentation file or target is named. Start by checking the repository's existing build documentation and CMake setup against the Termux commands, then use the pthreadpool.h sample and gcc test as a validation path. Done means the relevant Termux compilation guidance is placed in the appropriate documentation and can be followed successfully.

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