--enable-debug-flags patch seems to have broken non-GNU make

[Loren James Rittle]

In particular, BSD make.  In particular, the change to acinclude.m4
which switched: AC_LINK_FILES constructs to AC_SUBST.  It might be
that adding $srcdir to the paths is enough; however, I have tested
nothing.  Noted in daily regression test logs.  I will install
the obvious fix once I find it (and test it).

Regards,
Loren

(PS, been away from gcc hacking for a while.  Looking at the new
parser drew me back, Thanks Mark! ;-)