python3Packages.grpcio: add patch to fix armv6l build

Add a patch to fix the libatomic check, which was broken for platforms that
actually require libatomic (pretty much only armv6l). The patch has been
submitted upstream.

pkgs/development/python-modules/grpcio/default.nix

@@ -1,5 +1,6 @@
 { lib, stdenv
 , buildPythonPackage
+, fetchpatch
 , grpc
 , six
 , protobuf
@@ -17,6 +18,15 @@ buildPythonPackage rec {
   inherit (grpc) src version;
   pname = "grpcio";
 
+  patches = [
+    # Fix build on armv6l
+    # https://github.com/grpc/grpc/pull/30401
+    (fetchpatch {
+      url = "https://github.com/grpc/grpc/commit/65dc9f3edeee4c2d0e9b30d5a3ee63175437bea3.patch";
+      hash = "sha256-pS4FsCcSjmjSs3J5Y96UonkxqPwfpkyhrEM0t6HaMd0=";
+    })
+  ];
+
   outputs = [ "out" "dev" ];
 
   nativeBuildInputs = [ cython pkg-config ];