Is there routine in standard BLAS or LAPACK to set strictly-upper triangular part (the part above the diagonal) of a matrix to alpha?
I do not want to change diagonal elements so
laset is not a good candidate.
There are a bunch of useful functions missing in BLAS/LAPACK, for example the $ax+by \rightarrow y$ operation. The easiest way to get this functionality is to search for a similar BLAS/LAPACK routine, pick its source code, rename the function and extend its functionality to your needs.