cc/gcc: Add CUSTOM version and CUSTOM_LOCATION config options and GetCustom

CUSTOM_LOCATION config options only presented in menuconfig if component
CUSTOM version selected.

Signed-off-by: "David Holsgrove" <david.holsgrove@xilinx.com>
[yann.morin.1998@free.fr: don't patch custom directory location]
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Message-Id: <f2272ac0f37cedd0bb91.1349931194@localhost.localdomain>
PatchWork-Id: 190787

 reporter_name="Nye Liu"

 reporter_url="http://sourceware.org/ml/crossgcc/2008-10/msg00046.html"

 reporter_comment=""