Fix build: Do not return stack temporary.

Bug: b/139528538
Change-Id: I11d25399f582393ede13cbd8349c79cb3fdf4053
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/38608
Reviewed-by: Ben Clayton <bclayton@google.com>
Tested-by: Ben Clayton <bclayton@google.com>
diff --git a/src/Vulkan/VkStringify.cpp b/src/Vulkan/VkStringify.cpp
index 5fb4a2b..61ab208 100644
--- a/src/Vulkan/VkStringify.cpp
+++ b/src/Vulkan/VkStringify.cpp
@@ -464,10 +464,10 @@
 	else
 	{
 		WARN("Stringify(VkStructureType v) is out of date. Please update it to match vulkan/vulkan_core.h");
-		return std::to_string(value).c_str();
+		return "";
 	}
 #else // if not debug:
-	return std::to_string(value).c_str();
+	return "";
 #endif
 }