gcc-configure: Render --with-local-prefix harmless

gcc-configure: Render --with-local-prefix harmless

this option by default points to /usr/local no matter
what so we cant let it sit on sidelines otherwise it
will access host machine's /usr/local which may not
be desired. So disable this option. This also helps in making
gcc's shared state more consistent

Signed-off-by: Khem Raj <raj.khem@gmail.com>