Attach the datalayout before optimizing the LLVM module (#4761)

We should always set the `datalayout` when we run the optimization
pipeline on the LLVM IR module.

third_party/amd/backend/compiler.py

@@ -235,6 +235,7 @@ def make_llir(src, metadata, options):
         context = llvm.context()
         llvm_mod = llvm.to_module(mod, context)
         amd.attach_target_triple(llvm_mod)
+        llvm.attach_datalayout(llvm_mod, amd.TARGET_TRIPLE, options.arch, '')
 
         # Set various control constants on the LLVM module so that device
         # libraries can resolve references to them.