dev-util/glslang: add glslang package

Add glslang package, Khronos reference front-end for GLSL and ESSL, and sample SPIR-V
generator.

BUG=chromium:936705
TEST=emerge-nami glslang

Change-Id: Iba30c1e5eaef73d0079b7b6c4b57f64597039eeb
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/overlays/portage-stable/+/2506729
Reviewed-by: Ilja H. Friedel <ihf@chromium.org>
Reviewed-by: Benjamin Gordon <bmgordon@chromium.org>
Tested-by: Po-Hsien Wang <pwang@chromium.org>
Auto-Submit: Po-Hsien Wang <pwang@chromium.org>
Commit-Queue: Po-Hsien Wang <pwang@chromium.org>
4 files changed