niv nixpkgs-mozilla: update 05101591 -> 6070a8ee (#2849)

## Changelog for nixpkgs-mozilla:
Branch: master
Commits: [mozilla/nixpkgs-mozilla@05101591...6070a8ee](mozilla/nixpkgs-mozilla@0510159...6070a8e)

* [`2f03e7af`](mozilla/nixpkgs-mozilla@2f03e7a) Gecko: Make jsdoc an argument, and add fzf.
* [`e18c8960`](mozilla/nixpkgs-mozilla@e18c896) Gecko: Use stdenv's clang for clang paths.
* [`c0912b50`](mozilla/nixpkgs-mozilla@c0912b5) Gecko: fix libclang-path to avoid adding /lib twice.
* [`d41cea62`](mozilla/nixpkgs-mozilla@d41cea6) Rust: Export the manifest file under /nix-support.
* [`ad40e66f`](mozilla/nixpkgs-mozilla@ad40e66) cbindgen: update 0.13.1 -> 0.14.3.
* [`518e6a68`](mozilla/nixpkgs-mozilla@518e6a6) Replace self.lib by super.lib.
* [`9b9616a5`](mozilla/nixpkgs-mozilla@9b9616a) Gecko: Update how we extract gcc from the stdenv.
* [`cd53a47b`](mozilla/nixpkgs-mozilla@cd53a47) Gecko: Add m4 as a dependency.
* [`1295f347`](mozilla/nixpkgs-mozilla@1295f34) Remove outdated valgrind
* [`6070a8ee`](mozilla/nixpkgs-mozilla@6070a8e) Gecko: Add Clang12 in the compiler-overlay as it is required for clang-format.

nix/sources.json

@@ -129,10 +129,10 @@
         "homepage": null,
         "owner": "mozilla",
         "repo": "nixpkgs-mozilla",
-        "rev": "0510159186dd2ef46e5464484fbdf119393afa58",
-        "sha256": "1c6r5ldkh71v6acsfhni7f9sxvi7xrqzshcwd8w0hl2rrqyzi58w",
+        "rev": "6070a8ee799f629cb1d0004821f77ceed94d3992",
+        "sha256": "1lv3bh83f3f6caq5lk6bgpbq8zdd2xpw54xryccg1mxx8l5dadmq",
         "type": "tarball",
-        "url": "https://github.com/mozilla/nixpkgs-mozilla/archive/0510159186dd2ef46e5464484fbdf119393afa58.tar.gz",
+        "url": "https://github.com/mozilla/nixpkgs-mozilla/archive/6070a8ee799f629cb1d0004821f77ceed94d3992.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
     "ocaml-vlq": {