system: build for riscv64-unknown-linux-gnu (#10228)

* system: add support for riscv64-unknown-linux-gnu

* maintainers: upload riscv64-linux-gnu

* doc: add riscv64-linux to supported platforms

doc/manual/src/contributing/hacking.md

@@ -144,6 +144,7 @@ Nix can be built for various platforms, as specified in [`flake.nix`]:
 - `aarch64-darwin`
 - `armv6l-linux`
 - `armv7l-linux`
+- `riscv64-linux`
 
 In order to build Nix for a different platform than the one you're currently
 on, you need a way for your current Nix installation to build code for that
@@ -166,7 +167,10 @@ or for Nix with the [`flakes`] and [`nix-command`] experimental features enabled
 $ nix build .#packages.aarch64-linux.default
 ```
 
-Cross-compiled builds are available for ARMv6 (`armv6l-linux`) and ARMv7 (`armv7l-linux`).
+Cross-compiled builds are available for:
+- `armv6l-linux`
+- `armv7l-linux`
+- `riscv64-linux`
 Add more [system types](#system-type) to `crossSystems` in `flake.nix` to bootstrap Nix on unsupported platforms.
 
 ### Building for multiple platforms at once

flake.nix

@@ -31,6 +31,7 @@
       crossSystems = [
         "armv6l-unknown-linux-gnueabihf"
         "armv7l-unknown-linux-gnueabihf"
+        "riscv64-unknown-linux-gnu"
         "x86_64-unknown-netbsd"
         "x86_64-w64-mingw32"
       ];
@@ -253,6 +254,7 @@
           # Cross
           self.hydraJobs.binaryTarballCross."x86_64-linux"."armv6l-unknown-linux-gnueabihf"
           self.hydraJobs.binaryTarballCross."x86_64-linux"."armv7l-unknown-linux-gnueabihf"
+          self.hydraJobs.binaryTarballCross."x86_64-linux"."riscv64-unknown-linux-gnu"
         ];
         installerScriptForGHA = installScriptFor [
           # Native
@@ -261,6 +263,7 @@
           # Cross
           self.hydraJobs.binaryTarballCross."x86_64-linux"."armv6l-unknown-linux-gnueabihf"
           self.hydraJobs.binaryTarballCross."x86_64-linux"."armv7l-unknown-linux-gnueabihf"
+          self.hydraJobs.binaryTarballCross."x86_64-linux"."riscv64-unknown-linux-gnu"
         ];
 
         # docker image with Nix inside

maintainers/upload-release.pl

@@ -171,6 +171,10 @@ eval {
     downloadFile("binaryTarballCross.x86_64-linux.armv7l-unknown-linux-gnueabihf", "1");
 };
 warn "$@" if $@;
+eval {
+    downloadFile("binaryTarballCross.x86_64-linux.riscv64-linux-gnu", "1");
+};
+warn "$@" if $@;
 downloadFile("installerScript", "1");
 
 # Upload docker images to dockerhub.