Add a compiler option to rewrite vec/mat constructors If one of the parameters is a vec/mat, expand it into scalars. This is to work around Linux NVIDIA/AMD and Mac NVIDIA driver bugs. BUG=angle:695 TEST=webgl conformance test Change-Id: I35e1e25167d99f873dcb03bfb57a30e84b1aeed5 Reviewed-on: https://chromium-review.googlesource.com/207479 Reviewed-by: Jamie Madill <jmadill@chromium.org> Tested-by: Zhenyao Mo <zmo@chromium.org>