Bump LLVM to 8 (#649)

Author: pxl-th

Project.toml

@@ -44,7 +44,7 @@ GPUCompiler = "0.26.5"
 HIP_jll = "5.4"
 KernelAbstractions = "0.9.2"
 LLD_jll = "14, 15, 16"
-LLVM = "7"
+LLVM = "7, 8"
 LLVM_jll = "14, 15, 16"
 Preferences = "1"
 PrettyTables = "2"