less than ideal Makefile

[Loren James Rittle]

FYI, the Makefile(s) under libstdc++-v3 appear broken to me but they
could be correct according to convention.  Although it would be the
opposite convention used in the compiler directory where the motto is
that "one can never be forced to rebuild enough after what looks like
a trivial update to a file my port doesn't even use". ;-)

If I save a change to include/bits/fstream.tcc and run gmake-3.79.1 in
$obj, the correct parts of the library are not rebuilt unless I
explicitly remove $obj/src/misc-inst.lo.

Regards,
Loren