gnu: Add libomp-8.

* gnu/packages/llvm.scm (libomp-8): New variable.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

gnu/packages/llvm.scm

@@ -1069,6 +1069,23 @@ (define-public clang-8
                    "0ihnbdl058gvl2wdy45p5am55bq8ifx8m9mhcsgj9ax8yxlzvvvh"
                    #:patches '("clang-8.0-libc-search-path.patch")))
 
+(define-public libomp-8
+  (package
+    (inherit libomp-9)
+    (version (package-version llvm-8))
+    (source (origin
+              (method url-fetch)
+              (uri (llvm-uri "openmp" version))
+              (sha256
+               (base32
+                "0b3jlxhqbpyd1nqkpxjfggm5d9va5qpyf7d4i5y7n4a1mlydv19y"))
+              (file-name (string-append "libomp-" version ".tar.xz"))))
+    (native-inputs
+     (modify-inputs (package-native-inputs libomp-9)
+       (replace "clang" clang-8)
+       (replace "llvm" llvm-8)))
+    (license license:ncsa)))
+
 (define-public clang-toolchain-8
   (make-clang-toolchain clang-8))