[MLton] PowerPC .deb built

[Stephen Weeks]

> PS. The include directory is read-only for some reason:
>   W: mlton: non-standard-dir-perm usr/lib/mlton/include/ 0777 != 0755
>   W: mlton: non-standard-file-perm usr/lib/mlton/include/assert.h 0444 != 0644

A few weeks back I monkeyed around with the permissions on
build/lib/include to prevent accidental modification of those files.
However my attempt appears to have been more trouble than it was
worth, as it caused problems, including the one you mention here.  I
took out the change.  Let us know if your next build still has
problems.