No problem, and thanks anyway for the report. FWIW, we're aiming to change soon to a more R-like Subversion set-up, with all development happening in pkg/Matrix/ and changes being ported to branches/Matrix-x-y-branch/ as needed.
Indeed, branches/Matrix_1.7-0_branch works well with OpenBSD make! Sorry I didn't notice it and only checked pkg/Matrix.
By any chance, is this issue already fixed in branches/Matrix_1.7-0_branch/, which will be merged soon into pkg/Matrix/ (our "trunk")?