CompatHelper: bump compat for LLVM to 8, (keep existing compat) (#69)

Co-authored-by: CompatHelper Julia <compathelper_noreply@julialang.org>

Author: github-actions[bot]

Project.toml

@@ -22,7 +22,7 @@ Clang = "0.14, 0.17.4, 0.18"
 CxxWrap = "0.14, 0.16"
 GPUCompiler = "0.23, 0.24, 0.25, 0.26"
 JSON = "0.21.4"
-LLVM = "6, 7"
+LLVM = "6, 7, 8"
 LinearAlgebra = "1"
 Pkg = "1"
 ProgressMeter = "1.7"