Needed when building atlas/zimtool.It fixes this error:
```
/usr/bin/ld: png17/libpng17.a(pngrutil.c.o): in function `png_read_process_IDAT':
pngrutil.c:(.text+0x548c): undefined reference to `png_init_filter_functions_neon' collect2: error: ld returned 1 exit status
make[2]: *** [CMakeFiles/zimtool.dir/build.make:134: build/zimtool] Error 1
make[1]: *** [CMakeFiles/Makefile2:128: CMakeFiles/zimtool.dir/all] Error 2 make[1]: *** Waiting for unfinished jobs....
```