dev-lang/ghc: add github upstream metadata

Signed-off-by: Sam James <sam@gentoo.org>

dev-lang/ghc/metadata.xml

@@ -13,4 +13,7 @@
 		<flag name="gmp">Use <pkg>dev-libs/gmp</pkg> for integer operations (works faster, but an external depend).</flag>
 		<flag name="numa">Enable NUMA thread balancing policy using <pkg>sys-process/numactl</pkg>.</flag>
 	</use>
+	<upstream>
+		<remote-id type="github">ghc/ghc</remote-id>
+	</upstream>
 </pkgmetadata>