Include vulkan_win32.h only for Windows

src/VmaUsage.h

diff --git a/src/VmaUsage.h b/src/VmaUsage.h
index 527c897..906d6b9 100644
--- a/src/VmaUsage.h
+++ b/src/VmaUsage.h
@@ -97,7 +97,10 @@
 #endif
 
 #include <vulkan/vulkan.h>
+
+#ifdef _WIN32
 #include <vulkan/vulkan_win32.h>
+#endif  // #ifdef _WIN32
 
 #include "vk_mem_alloc.h"