llvm: create all versioned symlinks for libLLVM on darwin

Apply eb31e481475 to older versions where applicable.

pkgs/development/compilers/llvm/6/llvm.nix

@@ -21,11 +21,13 @@ let
 
   src = fetch "llvm" "1qpls3vk85lydi5b4axl0809fv932qgsqgdgrk098567z4jc7mmn";
 
-  # Used when creating a version-suffixed symlink of libLLVM.dylib
-  shortVersion = with stdenv.lib;
-    concatStringsSep "." (take 2 (splitString "." release_version));
+  # Used when creating a versioned symlinks of libLLVM.dylib
+  versionSuffixes = with stdenv.lib;
+    let parts = splitString "." release_version; in
+    imap (i: _: concatStringsSep "." (take i parts)) parts;
+in
 
-in stdenv.mkDerivation (rec {
+stdenv.mkDerivation (rec {
   name = "llvm-${version}";
 
   unpackPhase = ''
@@ -133,8 +135,9 @@ in stdenv.mkDerivation (rec {
   + optionalString (stdenv.isDarwin && enableSharedLibraries) ''
     substituteInPlace "$out/lib/cmake/llvm/LLVMExports-${if debugVersion then "debug" else "release"}.cmake" \
       --replace "\''${_IMPORT_PREFIX}/lib/libLLVM.dylib" "$lib/lib/libLLVM.dylib"
-    ln -s $lib/lib/libLLVM.dylib $lib/lib/libLLVM-${shortVersion}.dylib
-    ln -s $lib/lib/libLLVM.dylib $lib/lib/libLLVM-${release_version}.dylib
+    ${stdenv.lib.concatMapStringsSep "\n" (v: ''
+      ln -s $lib/lib/libLLVM.dylib $lib/lib/libLLVM-${v}.dylib
+    '') versionSuffixes}
   '';
 
   doCheck = stdenv.isLinux && (!stdenv.isi686);