meson: disable strchrnul on Darwin

It is not available on older versions of macOS so it will crash.

meson.build

@@ -2548,7 +2548,7 @@ config_host_data.set('HAVE_COPY_FILE_RANGE', cc.has_function('copy_file_range'))
 config_host_data.set('HAVE_GETIFADDRS', cc.has_function('getifaddrs'))
 config_host_data.set('HAVE_GLIB_WITH_SLICE_ALLOCATOR', glib_has_gslice)
 config_host_data.set('HAVE_OPENPTY', cc.has_function('openpty', dependencies: util))
-config_host_data.set('HAVE_STRCHRNUL', cc.has_function('strchrnul'))
+config_host_data.set('HAVE_STRCHRNUL', cc.has_function('strchrnul') and host_os != 'darwin')
 config_host_data.set('HAVE_SYSTEM_FUNCTION', cc.has_function('system', prefix: '#include <stdlib.h>'))
 if rbd.found()
   config_host_data.set('HAVE_RBD_NAMESPACE_EXISTS',