- Make HAVE_VULKAN an option so that it can be disabled

Had to compile on a Mac with no MoltenVK and no Vulkan SDK.

CMakeLists.txt

@@ -155,7 +155,7 @@ target_architecture(ZDOOM_TARGET_ARCH)
 
 if( ${ZDOOM_TARGET_ARCH} MATCHES "x86_64" )
 	set( HAVE_VM_JIT ON )
-	set( HAVE_VULKAN ON )
+	option (HAVE_VULKAN "Enable Vulkan support" ON)
 endif()
 
 # no, we're not using external asmjit for now, we made too many modifications to our's.

src/posix/cocoa/i_video.mm

@@ -355,8 +355,9 @@ public:
 
 	~CocoaVideo()
 	{
+#ifdef HAVE_VULKAN
 		delete m_vulkanDevice;
-
+#endif
 		ms_window = nil;
 	}
 
@@ -367,6 +368,7 @@ public:
 
 		SystemBaseFrameBuffer *fb = nullptr;
 
+#ifdef HAVE_VULKAN
 		if (ms_isVulkanEnabled)
 		{
 			const NSRect contentRect = [ms_window contentRectForFrameRect:[ms_window frame]];
@@ -421,6 +423,7 @@ public:
 			}
 		}
 		else
+#endif
 		{
 			SetupOpenGLView(ms_window);
 		}