Update package version to 20.1.8

pkg.info

@@ -1,6 +1,6 @@
 name: llvm
 description: A collection of modular and reusable compiler and toolchain technologies
-version: 20.1.7
+version: 20.1.8
 url: https://llvm.org
 license: Apache2-with-llvm-exception
 architecture: any