[vulkan] Implement external semaphore support for Fuchsia

This corresponds to the VK_FUCHSIA_external_semaphore extension
which uses a Zircon event object to communicate across processes.

Bug: b/140421726
Change-Id: I47b235d4ff7d787491738422bda6fdf853803ab7
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/35969
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Tested-by: David Turner <digit@google.com>
diff --git a/src/Vulkan/VkConfig.h b/src/Vulkan/VkConfig.h
index 9badfd8..ddb8d89 100644
--- a/src/Vulkan/VkConfig.h
+++ b/src/Vulkan/VkConfig.h
@@ -88,4 +88,8 @@
 #define SWIFTSHADER_EXTERNAL_SEMAPHORE_LINUX_MEMFD     1
 #endif
 
+#if VK_USE_PLATFORM_FUCHSIA
+#define SWIFTSHADER_EXTERNAL_SEMAPHORE_ZIRCON_EVENT  1
+#endif
+
 #endif // VK_CONFIG_HPP_