meson: Use Check=True only for the last nm process try
Without this nm invocation would fail if argument is not supported and would not try the next argument collection.
Also I wasn't sure about the "stderr=subprocess.DEVNULL" vs "stderr=subprocess.STDOUT" so I've left it as is, but I don't know what is expected.
It may also prove useful to replicate this change to librsvg as this change comes from them ( a5bc5338)
cc: @amyspark