Hi!

Thanks for the patch and the perfect comment.

The only thing I tweaked was the commit message, to reflect the 
‘what’ rather than (just) the ‘why’:

    * gnu/packages/sml.scm (smlnj): Replace INVOKE with SYSTEM
    which has more favourable signal dispositions.

Tested on a Guix System that could reproduce the original bug & 
pushed as 62da327848311a75723f16642c20d2925919237e.

Kind regards,

T G-R