Update on "[ET-VK] Fix OSS build + separate test build into its own CMakeLists.txt"

## Context

As title. In the next diff, the vulkan test binary will be added to CI.

Differential Revision: [D57747739](https://our.internmc.facebook.com/intern/diff/D57747739)

[ghstack-poisoned]

Author: SS-JIA

backends/vulkan/main.cpp

@@ -0,0 +1,7 @@
+#include <iostream>
+
+int main(int argc, char** argv)
+{
+    std::cout << "Hello World!" << std::endl;
+    return 0;
+}

backends/vulkan/test/CMakeLists.txt

@@ -17,9 +17,14 @@
 cmake_minimum_required(VERSION 3.19)
 project(executorch)
 
-find_package(executorch CONFIG REQUIRED)
+find_package(executorch CONFIG REQUIRED COMPONENTS vulkan_backend)
 find_package(GTest CONFIG REQUIRED)
 
+# Only build tests if Vulkan was compiled
+find_library(LIB_VULKAN_BACKEND vulkan_backend)
+
+if(LIB_VULKAN_BACKEND)
+
 if(NOT EXECUTORCH_ROOT)
   set(EXECUTORCH_ROOT ${CMAKE_CURRENT_SOURCE_DIR}/../../..)
 endif()
@@ -80,3 +85,5 @@ target_link_libraries(
                                   test_shaderlib
 )
 target_compile_options(vulkan_compute_api_test PRIVATE ${VULKAN_CXX_FLAGS})
+
+endif()

runtime/core/portable_type/targets.bzl

@@ -26,7 +26,6 @@ def define_common_targets():
         visibility = [
             "//executorch/runtime/core/exec_aten/...",
             "//executorch/runtime/core/portable_type/test/...",
-            "//executorch/backends/...",
         ],
         exported_deps = [
             ":scalar_type",

test/run_oss_cpp_tests.sh

@@ -27,7 +27,12 @@ build_and_run_test() {
   local test_dir=$1
   cmake "${test_dir}" -Bcmake-out/"${test_dir}" -DCMAKE_INSTALL_PREFIX=cmake-out
   cmake --build cmake-out/"${test_dir}" -j9
-  for t in cmake-out/"${test_dir}"/*test; do ./"$t"; done
+
+  for t in cmake-out/"${test_dir}"/*test; do
+    if [ -e $t ]; then
+      ./"$t";
+    fi
+  done
 }
 
 probe_tests() {