Require fixed workgroup size declaration

Fix 2479.

Test/negativeWorkGroupSize.comp

@@ -0,0 +1,12 @@
+#version 460
+
+void fn(){
+    uvec3 wgs = gl_WorkGroupSize; // error: fixed workgroup size has not been declared
+}
+
+layout(local_size_x = 64) in; // declare workgroup size
+
+void main(){
+    fn();
+    uvec3 wgs = gl_WorkGroupSize; // valid
+}