scripts/build/internals.sh: Always use binary wrapper under BSD/MacOS

The shell wrapper script uses a nonportable call to readlink.
Thus, always use the binary wrapper under BSD/MacOS.

yann.morin.1998@anciens.enib.fr:
Use 'case' instead of 'if'.

# Compute IA-64-specific values

CT_DoArchTupleValues() {

    # The architecture part of the tuple:

    CT_TARGET_ARCH="${CT_ARCH}"

}