Avoid using OPENGL_gl_LIBRARY

[RainerKuemmerle]

Relates: #573

[codecov]

Codecov Report

Merging #574 (513d815) into master (118f71c) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #574   +/-   ##
=======================================
  Coverage   46.73%   46.73%           
=======================================
  Files         271      271           
  Lines       10775    10775           
=======================================
  Hits         5036     5036           
  Misses       5739     5739           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 118f71c...513d815. Read the comment docs.