[PATCH, libgfortran] Remove AM_MAKEFLAGS.

[Steve Ellcey]

> Are you still using an old version of GNU make?
> 
> GCC requires GNU make 3.79.1 or later. If the make bug is fixed in 3.97.1 we 
> don't care, and anyone experiencing problems should upgrade. I believe that 
> version was picked for a reason, though I'm not sure of the details.
> 
> Paul

Woops, forgot to include that information.  I updated to 3.80 gnu make and
it didn't help any.  I still needed to set AM_MAKEFLAGS.

Steve Ellcey
sje@cup.hp.com