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

 # Wrapper to build the debug facilities

 # List all debug facilities, and parse their scripts

 CT_DEBUG_FACILITY_LIST=

 for f in "${CT_LIB_DIR}/scripts/build/debug/"*.sh; do

     _f="$(basename "${f}" .sh)"

     _f="${_f#???-}"

     __f="CT_DEBUG_${_f}"

     if [ "${!__f}" = "y" ]; then

         CT_DoLog DEBUG "Enabling debug '${_f}'"

         . "${f}"

         CT_DEBUG_FACILITY_LIST="${CT_DEBUG_FACILITY_LIST} ${_f}"

     else

         CT_DoLog DEBUG "Disabling debug '${_f}'"

     fi

 done

 # Download the debug facilities

 do_debug_get() {

     for f in ${CT_DEBUG_FACILITY_LIST}; do

         do_debug_${f}_get

     done

 }

 # Extract and patch the debug facilities

 do_debug_extract() {

     for f in ${CT_DEBUG_FACILITY_LIST}; do

         do_debug_${f}_extract

     done

 }

 # Build the debug facilities

 do_debug() {

     for f in ${CT_DEBUG_FACILITY_LIST}; do

         do_debug_${f}_build

     done

 }