Change in $(MFLAGS) format breaks automake-generated rules

[Stefano Lattarini]

Few automake-generated recipes have the necessity to determine at
runtime whether a particular make mode/option is active (e.g., '-k'
or '-n').  To do so, they analyze the content of the $(MFLAGS) make
variable.

But the exact format of this variable has been changed in the
development version of GNU make, thus breaking those recipes:

   # With make 3.82, compiled from official tarball:
   $ make -f- <<<'all:; @echo $(MFLAGS)' -I none
   -I none

   # With development version of make:
   $ make -f- <<<'all:; @echo $(MFLAGS)' -I none
   -Inone

Is there a reason behind this change?  If not, could it be reverted?
No big deal if the change is intended, as I can certainly and easily
improve the Automake recipes instead.

Thanks,
  Stefano