[RFC] Update minimum make version to 3.81

[Florian Weimer]

On 06/11/2016 12:27 AM, Roland McGrath wrote:
> eval is a pretty horrible feature and I'd probably object to introducing
> any uses of it into libc's makefiles.  We already have lots of things that
> might have been done that way, but are instead done with generated makefiles.

I would like to put this into malloc/Makefile:

$(foreach t,$(tests),$(eval CFLAGS-$t.c += -DTEST_NO_MALLOPT))

What's the alternative for adding a -D flag to every test compilation in 
a subdirectory?

Thanks,
Florian