scripts: refine static linking check to better guide the user

The current mechanism to check if static linking is possible, and the mesage
displayed on failure, can be puzzling to the unsuspecting user.

Also, the current implementation is not using the existing infrastructure,
and is thus difficult to enhance with new tests.

So, switch to using the standard CT_DoExecLog infra, and use four tests to
check for the host compiler:
- check we can run it
- check it can build a trivial program
- check it can statically link that program
- check if it statically link with libstdc++

That should cover most of the problems. Hopefully.

(At the same time, fix a typo in a comment)

Signed-off-by: Daniel Price <daniel.price@gmail.com>
[yann.morin.1998@free.fr: split original patch for self-contained changes]
[yann.morin.1998@free.fr: use steps to better see gcc's output]
[yann.morin.1998@free.fr: commit log]
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Message-Id: <163f86b5216fc08c672a.1353459722@nipigon.dssd.com>
Patchwork-Id: 200536

# Compute powerpc-specific values

CT_DoArchTupleValues () {

    # The architecture part of the tuple, override only for 64-bit

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

        CT_TARGET_ARCH="powerpc64"

    fi

    # Only override values when ABI is not the default

    case "${CT_ARCH_powerpc_ABI}" in

        eabi)

            # EABI is only for bare-metal, so libc ∈ [none,newlib]

            CT_TARGET_SYS="eabi"

            ;;

        spe)

            case "${CT_LIBC}" in

                none|newlib)    CT_TARGET_SYS="spe";;

                *glibc)         CT_TARGET_SYS="gnuspe";;

                uClibc)         CT_TARGET_SYS="uclibcgnuspe";;

            esac

            ;;

    esac

    # Add extra flags for SPE if needed

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

        CT_ARCH_TARGET_CFLAGS="-mabi=spe -mspe"

        CT_ARCH_CC_CORE_EXTRA_CONFIG="--enable-e500_double"

        CT_ARCH_CC_EXTRA_CONFIG="--enable-e500_double"

    fi

}