mesa: when linking a shader program, make sure all the shaders compiled OK

cherry-picked from master

src/mesa/shader/slang/slang_link.c

 
    _mesa_clear_shader_program_data(ctx, shProg);
 
+   /* check that all programs compiled successfully */
+   for (i = 0; i < shProg->NumShaders; i++) {
+      if (!shProg->Shaders[i]->CompileStatus) {
+         link_error(shProg, "linking with uncompiled shader\n");
+         return;
+      }
+   }
+
    shProg->Uniforms = _mesa_new_uniform_list();
    shProg->Varying = _mesa_new_parameter_list();