Failed to build with thread-safe option set on Android

Enabling thread-safe build results in compile error.
```
ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
```
Missing functions are `pthread_cancel` and `pthread_setcancelstate`

Platform
- HDF5 version: develop
- OS and version: Windows 11 Pro
- Compiler and version: android-ndk-27c
- Build system: CMake 3.30.5
- Any configure options you specified:
ONLY_SHARED_LIBS=ON
HDF5_ENABLE_THREADSAFE=ON
HDF5_BUILD_HL_LIB=ON
HDF5_BUILD_CPP_LIB=ON ALLOW_UNSUPPORTED=ON
- MPI library and version (parallel HDF5): OFF

**Additional context**
Add any other context about the problem here.