darwin.CF: Drop clang 7 workaround

pkgs/os-specific/darwin/swift-corelibs/corefoundation.nix

@@ -73,24 +73,7 @@ stdenv.mkDerivation {
 
   enableParallelBuilding = true;
 
-  # FIXME: Workaround for intermittent build failures of CFRuntime.c.
-  # Based on testing this issue seems to only occur with clang_7, so
-  # please remove this when updating the default llvm versions to 8 or
-  # later.
-  buildPhase = lib.optionalString true ''
-    for i in {1..1}; do
-        if ninja -j $NIX_BUILD_CORES; then
-            break
-        fi
-
-        echo >&2
-        echo "[$i/512] retrying build, workaround for #66811" >&2
-        echo "  With clang_7 the build of CFRuntime.c fails intermittently." >&2
-        echo "  See https://github.com/NixOS/nixpkgs/issues/66811 for more details." >&2
-        echo >&2
-        continue
-    done
-  '';
+  buildPhase = "ninja -j $NIX_BUILD_CORES";
 
   # TODO: their build system sorta kinda can do this, but it doesn't seem to work right now
   # Also, this includes a bunch of private headers in the framework, which is not what we want