cc/gcc: modify to build gcc-4.8-based cross-tools

Building cross-tool based on gcc-4.8 fails while "Installing
pass-2 core C compiler", because building libgcc.mvars needs
libbacktrace.a that gcc.sh doesn't build. This patch inserts
a few lines configuring, and making libbacktrace into gcc.sh
to build gcc-4.8-based cross-tools successfully.

Reported-by: Plotnikov Dmitry <leitz@ispras.ru>
Signed-off-by: Jongsung Kim <neidhard.kim@lge.com>
Message-Id: <201305031831.33395.neidhard.kim@lge.com>
Patchwork-Id: 241258

# Super-H specific configuration file

choice

    bool

    prompt "Variant"

config ARCH_SH_SH3

    bool

    prompt "sh3"

config ARCH_SH_SH4

    bool

    prompt "sh4"

config ARCH_SH_SH4A

    bool

    prompt "sh4a"

endchoice

config ARCH_SH_VARIANT

    string

    default "sh3"   if ARCH_SH_SH3

    default "sh4"   if ARCH_SH_SH4

    default "sh4a"  if ARCH_SH_SH4A