Build QNN backend tests with EXTENSION_TENSOR, mark option as required (#18140)

The QNN backend references extension_tensor and thus requires it to be
built. This PR makes two changes:

* Build extension_tensor in the backend test flow (unbreaks QNN jobs).
* Mark the option as required to build QNN to give a nicer error
message.

Author: GregoryComer

.ci/scripts/test_backend.sh

@@ -46,7 +46,7 @@ if [[ "$FLOW" == *qnn* ]]; then
     export LD_LIBRARY_PATH"=$QNN_X86_LIB_DIR:$QNN_SDK_ROOT/lib/x86_64-linux-clang/:${LD_LIBRARY_PATH:-}"
 
     # TODO Get SDK root from install scripts
-    EXTRA_BUILD_ARGS+=" -DEXECUTORCH_BUILD_QNN=ON -DQNN_SDK_ROOT=$QNN_SDK_ROOT"
+    EXTRA_BUILD_ARGS+=" -DEXECUTORCH_BUILD_QNN=ON -DQNN_SDK_ROOT=$QNN_SDK_ROOT -DEXECUTORCH_BUILD_EXTENSION_TENSOR=ON"
 fi
 
 if [[ "$FLOW" == *vulkan* ]]; then

tools/cmake/preset/default.cmake

@@ -338,6 +338,10 @@ check_required_options_on(
   IF_ON EXECUTORCH_ENABLE_EVENT_TRACER REQUIRES EXECUTORCH_BUILD_DEVTOOLS
 )
 
+check_required_options_on(
+  IF_ON EXECUTORCH_BUILD_QNN REQUIRES EXECUTORCH_BUILD_EXTENSION_TENSOR
+)
+
 check_required_options_on(
   IF_ON EXECUTORCH_ENABLE_BUNDLE_IO REQUIRES EXECUTORCH_BUILD_DEVTOOLS
 )