[PATCH 1/2] BZ#10375: Configure magic to use -U_FORTIFY_SOURCE if needed.

[Roland McGrath]

> > -CPPFLAGS-config = @CPPFLAGS@
> > +CPPFLAGS-config = @CPPUNDEFS@ @CPPFLAGS@
> 
> Is there a reason to prepend this rather than append it?  Appending it
> has the advantage of fixing the build for people who have
> _FORTIFY_SOURCE defined in their default build environment CPPFLAGS
> (which this currently detects but does not fix).

My logic was simply that this automatic addition is meant to counteract the
compiler default.  So it's in the earliest position to come closest to the
predefines.