games/devilutionX: update to 1.2.0

While here:

• set version correctly with -DVERSION_NUM=${PORTVERSION} (cmake)
• pet portclippy by using "_" prefix in local variable "MY_DEPENDS"

Changes:
https://github.com/diasurgical/devilutionX/releases/tag/1.2.0

Approved by: dbaio (mentor)
Differential Revision: https://reviews.freebsd.org/D29638