update : graphics/glm 0.9.8.4 > 0.9.8.5

Hi ports,

please find attached an update for glm to latest 0.9.8.5.
changes :
- typos about github vars
- removed gcc as compiler in profit of default clang
- enforced use of C++11 instead of default C++98

changelog :
https://github.com/g-truc/glm/releases/tag/0.9.8.5

built on AMD64. OK ? Comments ?

regards,
Jerome