Replace the bionic hack for a vfprintf leak with (roughly) the upstream fix.

Currently in bionic free and freedtoa are equivalent, but that's not true
of gdtoa. This makes it easier to test gdtoa without having to replace
everything. (Yes, I found this bug the hard way.)

Change-Id: I290823a2a0a83329def5f2719b349215ad0dbbde

Conflicts:
	libc/stdio/vfprintf.c