Fix compliation for musl or older glibc system
- Properly include
stdlib.h
wheneverEXIT_{FAILURE|SUCCESS}
orexit(3)
is used - Fallback implementation via
syscall(2)
ifcopy_file_range(2)
is not available - Fix compilation and tests when using the musl C standard library
- Add Alpine as CI target
Closes #126 (closed)