[lavapipe] Split fuchsia block in zircon / magma.

Change-Id: I41910d917912772cff83178906b890baab26a204
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/mesa/+/988079
Reviewed-by: John Bauman <jbauman@google.com>
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/mesa/+/1005912
Commit-Queue: Josh Gargus <jjosh@google.com>
diff --git a/src/vulkan/runtime/vk_semaphore.c b/src/vulkan/runtime/vk_semaphore.c
index 5e72140..a83852f 100644
--- a/src/vulkan/runtime/vk_semaphore.c
+++ b/src/vulkan/runtime/vk_semaphore.c
@@ -581,6 +581,7 @@
 #endif /* !defined(_WIN32) */
 
 #if defined(__Fuchsia__)
+#if defined(USE_MAGMA)
 
 VkResult
 vk_common_ImportSemaphoreZirconHandleFUCHSIA(VkDevice vk_device,
@@ -646,4 +647,6 @@
    return VK_SUCCESS;
 }
 
+#else /* Zircon */
+#endif  /* defined(USE_MAGMA) */
 #endif /* defined(__Fuchsia__) */