gnupatch: Don't fetch from cgit URLs with unstable hashes

cgit cannot serve patches with stable hashes, so store these patches
in-tree.  cgit community discussion about this problem:
https://lists.zx2c4.com/pipermail/cgit/2017-February/003470.html

We pull the patches in-tree rather than strip cgit footers with fetchpatch
because per https://github.com/NixOS/nixpkgs/pull/61471#issuecomment-493218587
dependencies of fetchpatch cannot use fetchpatch.

Verification that the only difference between the live page, the
patch committed here, and the version cached under the old hash at
tarballs.nixos.org is the cgit version footer:

$ curl -s -L http://tarballs.nixos.org/sha256/"$(nix-hash --type sha256 --to-base16 0iw0lk0yhnhvfjzal48ij6zdr92mgb84jq7fwryy1hdhi47hhq64)" > Allow_input_files_to_be_missing_for_ed-style_patches.patch
$ diff -U0 --label cgit-live <( curl -s -L https://git.savannah.gnu.org/cgit/patch.git/patch/?id=b5a91a01e5d0897facdd0f49d64b76b0f02b43e1 ) Allow_input_files_to_be_missing_for_ed-style_patches.patch
--- cgit-live
+++ Allow_input_files_to_be_missing_for_ed-style_patches.patch  2020-01-29 17:22:00.077312937 -0800
@@ -32 +32 @@
-cgit v1.2.1
+cgit v1.0-41-gc330

$ curl -s -L http://tarballs.nixos.org/sha256/"$(nix-hash --type sha256 --to-base16 1bpy16n3hm5nv9xkrn6c4wglzsdzj3ss1biq16w9kfv48p4hx2vg)" > CVE-2018-1000156.patch
$ diff -U0 --label cgit-live <( curl -s -L https://git.savannah.gnu.org/cgit/patch.git/patch/?id=123eaff0d5d1aebe128295959435b9ca5909c26d ) CVE-2018-1000156.patch
--- cgit-live
+++ CVE-2018-1000156.patch      2020-01-29 17:23:41.021116969 -0800
@@ -210 +210 @@
-cgit v1.2.1
+cgit v1.0-41-gc330

0 files changed, 0 insertions, 0 deletions