Retired biotechnology executive Henri A. Termeer, who built Genzyme Corp. into the largest US company specializing in drugs to treat rare genetic disorders, is donating $10 million to Massachusetts General Hospital to establish it as a world leader in personalized medicine. The new Henri and Belinda Termeer Center for Targeted Therapies will be aimed at bringing the emerging field into the forefront of treatment and research. Its initial focus will be on drugs tailored to the genetic makeup of tumors, especially breast cancers, lung cancers, and leukemias. Currently, there are few effective treatments for patients with less common types of the diseases.