[VK] Fix EnabledDeviceExtensions redefinition and drop on macOS build

Two local variables both named `EnabledDeviceExtensions` were declared in the same enclosing scope of `VulkanDevice::create`: one added by #1177 (mesh shader) and one added inside `#ifdef VK_EXT_SHADER_IMAGE_ATOMIC_INT64_EXTENSION_NAME` by #1195 (InterlockedOr). On platforms where the Vulkan SDK defines that macro (e.g. the macOS runner with Vulkan 1.4.335), clang rejects the file with `error: redefinition of 'EnabledDeviceExtensions' with a different type`.

Beyond the build break, the inner block also overwrote `DeviceInfo.enabledExtensionCount` and `ppEnabledExtensionNames` that the mesh-shader block had populated, silently dropping `VK_EXT_mesh_shader` whenever both extensions were available.

Append the AtomicInt64 extension to the single `EnabledDeviceExtensions` vector and assign the `DeviceInfo` extension fields once, after both blocks.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: alsepkow

lib/API/VK/Device.cpp

@@ -1315,22 +1315,19 @@ class VulkanDevice : public offloadtest::Device {
       Features.pNext = &MeshFeatures;
     }
 
-    DeviceInfo.enabledExtensionCount =
-        static_cast<uint32_t>(EnabledDeviceExtensions.size());
-    DeviceInfo.ppEnabledExtensionNames = EnabledDeviceExtensions.data();
-    DeviceInfo.pEnabledFeatures = &Features.features;
-    DeviceInfo.pNext = Features.pNext;
-
 #ifdef VK_EXT_SHADER_IMAGE_ATOMIC_INT64_EXTENSION_NAME
-    llvm::SmallVector<const char *, 1> EnabledDeviceExtensions;
     if (HasShaderImageAtomicInt64Ext &&
         FeaturesImageAtomicInt64.shaderImageInt64Atomics)
       EnabledDeviceExtensions.push_back(
           VK_EXT_SHADER_IMAGE_ATOMIC_INT64_EXTENSION_NAME);
-    DeviceInfo.enabledExtensionCount = EnabledDeviceExtensions.size();
-    DeviceInfo.ppEnabledExtensionNames = EnabledDeviceExtensions.data();
 #endif
 
+    DeviceInfo.enabledExtensionCount =
+        static_cast<uint32_t>(EnabledDeviceExtensions.size());
+    DeviceInfo.ppEnabledExtensionNames = EnabledDeviceExtensions.data();
+    DeviceInfo.pEnabledFeatures = &Features.features;
+    DeviceInfo.pNext = Features.pNext;
+
     VkDevice Device = VK_NULL_HANDLE;
     if (auto Err = VK::toError(
             vkCreateDevice(PhysicalDevice, &DeviceInfo, nullptr, &Device),