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

 CT_EXPERIMENTAL=y

 CT_LOCAL_TARBALLS_DIR="${HOME}/src"

 CT_SAVE_TARBALLS=y

 CT_LOG_EXTRA=y

 CT_ARCH_mips=y

 CT_TARGET_VENDOR="malta"

 CT_KERNEL_linux=y

 CT_KERNEL_V_2_6_38=y

 CT_BINUTILS_V_2_21_1a=y

 CT_CC_V_4_4_6=y

 # CT_CC_GCC_USE_GRAPHITE is not set

 CT_LIBC_EGLIBC_V_2_13=y

 CT_DEBUG_gdb=y

 # CT_GDB_GDBSERVER_STATIC is not set

 CT_GDB_V_7_2a=y

 CT_GMP_V_5_0_1=y

 CT_MPFR_V_3_0_0=y

 CT_TEST_SUITE_GCC=y