cc/gcc: allow CC_EXTRA_CONFIG_ARRAY on baremetal

The final bare-metal compiler is built using the core backend.
Currently the core uses the CC_CORE_EXTRA_CONFIG_ARRAY variable.

While this works as supposed to, this can leave the user puzzled
in the menuconfig, since all he can see is the core options, not
the final options.

Only show the core options if any of the core passes are needed,
and use the final options in the core-backend if we're issuing
the bare-metal compiler.

Signed-off-by: Cody P Schafer <dev@codyps.com>
[yann.morin.1998@free.fr: hide core options if no core pass needed;
use final option in core backend if issuing the bare-metal compiler]
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Message-Id: <22181e546ba746202489.1399688067@localhost>
Patchwork-Id: 347586

 reporter_name="Anthony Foiani <anthony.foiani@gmail.com>"

 reporter_url="http://sourceware.org/ml/crossgcc/2010-09/msg00100.html"

 reporter_comment="This is a sample config file for Freescale e500v2 processors (e.g., MPC8548,

 MPC8572). It uses eglibc (for e500/SPE patches) and a recent gcc (4.6.0,

 for e500v2 DPFP support) and will generate appropriate dual-precision

 floating point instructions by default.

 Note: If building a Linux kernel with this toolchain, you will want to make

 sure -mno-spe AND -mspe=no are passed to gcc to prevent SPE ABI/instructions

 from getting into the kernel (which is currently unsupported). At this time,

 the kernel build system properly passes those two options, but older kernels

 were only passing -mno-spe by default."