Make vulkan build as optional (google#4814)

Add option WITH_VULKAN, which is ON by default.
If set to OFF, packages OrbitTriggerCaptureVulkanLayer, OrbitVulkanLayer,
and VulkanTutorial won't be built

CMakeLists.txt

@@ -66,6 +66,7 @@ endif()
 set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
 
 option(WITH_GUI "Setting this option will enable the Qt-based UI client." ON)
+option(WITH_VULKAN "Setting this option will enable Vulkan" ON)
 
 # This is only for designated initializers
 if(WIN32)
@@ -127,9 +128,11 @@ else()
   find_package(libbase REQUIRED)
   find_package(liblog REQUIRED)
   find_package(libprocinfo REQUIRED)
-  find_package(volk REQUIRED)
-  find_package(VulkanHeaders REQUIRED)
-  find_package(vulkan-validationlayers REQUIRED)
+  if(WITH_VULKAN)
+    find_package(volk REQUIRED)
+    find_package(VulkanHeaders REQUIRED)
+    find_package(vulkan-validationlayers REQUIRED)
+  endif()
 endif()
 
 include("cmake/protobuf.cmake")
@@ -173,13 +176,15 @@ else()
   add_subdirectory(src/OrbitClientGgp)
   add_subdirectory(src/OrbitCaptureGgpClient)
   add_subdirectory(src/OrbitCaptureGgpService)
-  add_subdirectory(src/OrbitTriggerCaptureVulkanLayer)
-  add_subdirectory(src/OrbitVulkanLayer)
   add_subdirectory(src/ProcessService)
   add_subdirectory(src/TracepointService)
   add_subdirectory(src/UserSpaceInstrumentation)
-  add_subdirectory(src/VulkanTutorial)
   add_subdirectory(third_party/libunwindstack)
+  if(WITH_VULKAN)
+    add_subdirectory(src/OrbitTriggerCaptureVulkanLayer)
+    add_subdirectory(src/OrbitVulkanLayer)
+    add_subdirectory(src/VulkanTutorial)
+  endif()
 endif()
 
 add_subdirectory(src/Api)