cc/gcc: Make usage of --enable-target-optspace configurable

Optionally configure to compile gcc-internal libs with -Os.

yann.morin.1998@anciens.enib.fr:
Rename the config options, it is in the GCC /namespace/.

 # Compute IA-64-specific values

 CT_DoArchTupleValues() {

     # The architecture part of the tuple:

     CT_TARGET_ARCH="${CT_ARCH}"

 }