For all keywords already present, get correct when they could be identifiers, are reserved words, or are keywords, for all versions of ESSL and GLSL.

git-svn-id: https://cvs.khronos.org/svn/repos/ogl/trunk/ecosystem/public/sdk/tools/glslang@21282 e7fa87d3-cd2b-0410-9028-fcbf551c1848

Test/300layout.vert

@@ -43,3 +43,7 @@ void main()
     pos = p * (tblock.M1 + tblock.M2 + M4 + M3 + t2m);
     color = c * tblock.N1;
 }
+
+shared vec4 compute_only;  // ERROR
+
+layout(packed) uniform;