Fix build on windows when vulkan is not supported (#9439)

Co-authored-by: Sungun Park <sungunpark@google.com>

libs/filamentapp/CMakeLists.txt

@@ -37,9 +37,12 @@ set(SRCS
         src/IcoSphere.cpp
         src/MeshAssimp.cpp
         src/Sphere.cpp
-        src/VulkanPlatformHelper.cpp
 )
 
+if (FILAMENT_SUPPORTS_VULKAN)
+    list(APPEND SRCS src/VulkanPlatformHelper.cpp)
+endif()
+
 set(LIBS
         assimp
         camutils
@@ -79,7 +82,11 @@ endif()
 
 if (WIN32)
     list(APPEND SRCS src/NativeWindowHelperWindows.cpp)
-    list(APPEND SRCS src/VulkanPlatformHelperWindows.cpp)
+
+    if (FILAMENT_SUPPORTS_VULKAN)
+        list(APPEND SRCS src/VulkanPlatformHelperWindows.cpp)
+    endif()
+
     list(APPEND LIBS sdl2main)
 endif()