* lisp/progmodes/asm-mode.el: The value of fill-prefix ought to be nil
not "\t" so that fill-context-prefix can do its thing. In fact,
fill-prefix does not have to be set at all becuase asm-mode derives
from prog-mode and fill-prefix is set in simple.el.
* test/lisp/progmodes/asm-mode-tests.el: Add relevant test (bug#41064).
Copyright-paperwork-exempt: yes