Dynamic shadows with the ogles2 driver on OpenGL ES 3.0+ (#16661)

client/shaders/shadow/pass1_trans/opengl_vertex.glsl

@@ -1,8 +1,8 @@
 uniform mat4 LightMVP; // world matrix
 uniform vec4 CameraPos;
-varying vec4 tPos;
+VARYING_ vec4 tPos;
 #ifdef COLORED_SHADOWS
-varying vec3 varColor;
+VARYING_ vec3 varColor;
 #endif
 
 uniform float xyPerspectiveBias0;