libgltf: Append shader language version to the shader files

In general glTF shader files does not contain version
directives and in some case it make shader compiler
using GLSL 1.1 which leads to that the shader compiler
fails.
So we need to append the choosen version number which is
GLSL 1.3 in case of libgltf, but this also means that
from that point OpenGL 3.0 is the new reuirements since
GLSL 1.3 is available only from that version.

(cherry picked from commit c67026f27023008d124c8ab76533169f032b04f6)

Conflicts:
	external/libgltf/UnpackedTarball_libgltf.mk

Change-Id: Ic4382266432ea474aeb3e603b32a998b9aeed280
Reviewed-on: https://gerrit.libreoffice.org/10947
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>