Merge pull request #124929 from NixOS/backport-124918-to-release-21.05

[Backport release-21.05] newsflash: fix build

pkgs/applications/networking/feedreaders/newsflash/default.nix

@@ -35,6 +35,12 @@ stdenv.mkDerivation rec {
     hash = "sha256-qq8cZplt5YWUwsXUShMDhQm3RGH2kCEBk64x6bOa50E=";
   };
 
+  # https://github.com/CasualX/obfstr/blob/v0.2.4/build.rs#L5
+  # obfstr 0.2.4 fails to set RUSTC_BOOTSTRAP in its build script because cargo
+  # build scripts are forbidden from setting RUSTC_BOOTSTRAP since rustc 1.52.0
+  # https://github.com/rust-lang/rust/blob/1.52.0/RELEASES.md#compatibility-notes
+  RUSTC_BOOTSTRAP = 1;
+
   patches = [
     # Post install tries to generate an icon cache & update the
     # desktop database. The gtk setup hook drop-icon-theme-cache.sh