* make clean: 'rm -rf ...' instead of 'rm ... -r -f'
Only GNU rm supports flags after paths
* Scale2x: do not include malloc.h on FreeBSD
* Allow using system libevdev, use sdl2-config to find sdl2
+ extract the C++17 fs library name into a variable to allow overriding
(it's -lc++experimental on systems with LLVM's libc++ as the C++ lib)
