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'.

 This is NOT the official version of dialog.  This version has been

 significantly modified from the original.  It is for use by the Linux

 kernel configuration script.  Please do not bother Savio Lam with 

 questions about this program.