GPU: Do not allow GPU Shader builder when USD is enabled.

Linking GPU shader builder requires stubs for many functions of the USD library.
We don't want to rely on other modules to update the stubs for a tool that
is only used by GPU developers.

This patch raises an error when both WITH_GPU_SHADER_BUILDER and WITH_USD are
enabled. This reduces the maintenance of updating the stubs when USD API changes.

Reviewed By: LazyDodo

Differential Revision: https://developer.blender.org/D15422

CMakeLists.txt

@@ -1340,6 +1340,12 @@ else()
   list(APPEND GL_DEFINITIONS -DWITH_GL_PROFILE_CORE)
 endif()
 
+if (WITH_GPU_SHADER_BUILDER AND WITH_USD)
+  message(FATAL_ERROR
+    "Unable to compile WITH_GPU_SHADER_BUILDER and WITH_USD."
+  )
+endif()
+
 #-----------------------------------------------------------------------------
 # Configure Metal.
 if (WITH_METAL_BACKEND)