dev-db/postgresql: update metadata.xml

Author: Dave Hughes

dev-db/postgresql/metadata.xml

@@ -20,6 +20,10 @@
 		<flag name="llvm">
 			Add support for llvm JIT engine
 		</flag>
+		<flag name="pg-legacytimestamp">
+			Use double precision floating-point numbers instead of
+			64-bit integers for timestamp storage.
+		</flag>
 		<flag name="server">
 			Disable to build and install the clients and libraries
 			only.