Issue is solved. For information:

Had a support ticket in parallel.
Support confirmed that the devel rpm is missing in the SDK and suggested to install the
complete sources (mysql-5.5.60-0.39.12.1.src.rpm) instead.
However, we decided to use MySQL-devel-5.5.60-1.sles11.x86_64.rpm from mysql.com instead.

Regards
Dan