cc/gcc: add option to compile against static libstdc++, for gcc-4.4 and newer

Idea and know-how taken from CodeSourcery build script.

Normal build:
$ ldd arm-unknown-linux-uclibcgnueabi-gcc
linux-gate.so.1 => (0xb77f3000)
libstdc++.so.6 => /usr/lib/libstdc++.so.6 (0xb76e8000)
libc.so.6 => /lib/i686/cmov/libc.so.6 (0xb75a1000)
libm.so.6 => /lib/i686/cmov/libm.so.6 (0xb757a000)
/lib/ld-linux.so.2 (0xb77f4000)
libgcc_s.so.1 => /lib/libgcc_s.so.1 (0xb755c000)

CC_STATIC_LIBSTDCXX=y:
$ ldd arm-unknown-linux-uclibcgnueabi-gcc
linux-gate.so.1 => (0xb7843000)
libc.so.6 => /lib/i686/cmov/libc.so.6 (0xb76e6000)
/lib/ld-linux.so.2 (0xb7844000)

I made CC_STATIC_LIBSTDCXX default=y since I think
it is always desirable.

Signed-off-by: Johannes Stezenbach <js@sig21.net>

# Compute s390-specific values

CT_DoArchTupleValues() {

    # That's the only thing to override

    if [ "${CT_ARCH_64}" = "y" ]; then

        CT_TARGET_ARCH="s390x"

    fi

}