Squashed 'externals/glm/' content from commit 4fa38c7

git-subtree-dir: externals/glm
git-subtree-split: 4fa38c7a03df4064f9c4fff75f9d5a93f0049ae5
Merge commit '0.9.5.4' as 'externals/glm'
Using the subtree imported glm.
Update glm using the official repository as a subtree.