tlbuild: --enable-multiplatform

 
 7.1.8 '--enable-multiplatform'
 ------------------------------
 
 If enabled (as it is for the native TL build) and '--bindir=DIR' or
 '--libdir=DIR' are not specified, install executables and libraries in
 per-platform subdirectories of 'EPREFIX/bin' and 'EPREFIX/lib' where
 EPREFIX is the value given or implied for 'exec_prefix'.  In any case,
 the values for 'bindir' and 'libdir' are automatically propagated to all
 subdirectories.