Add arm6vl (rpi) build

flake.nix

@@ -23,6 +23,12 @@
           rustTarget = "aarch64-unknown-linux-musl";
         };
 
+        # Old Raspberry Pi's
+        "armv6l-linux" = {
+          crossSystemConfig = "armv6l-unknown-linux-musleabihf";
+          rustTarget = "arm-unknown-linux-musleabihf";
+        };
+
         "x86_64-windows" = {
           crossSystemConfig = "x86_64-w64-mingw32";
           rustTarget = "x86_64-pc-windows-gnu";
@@ -127,12 +133,15 @@
 
             # Required because ring crate is special. This also seems to have
             # fixed some issues with the x86_64-windows cross-compile :shrug:
-            TARGET_CC="${pkgsCross.stdenv.cc}/bin/${pkgsCross.stdenv.cc.targetPrefix}cc";
+            TARGET_CC = "${pkgsCross.stdenv.cc}/bin/${pkgsCross.stdenv.cc.targetPrefix}cc";
 
             CARGO_BUILD_TARGET = rustTarget;
             CARGO_BUILD_RUSTFLAGS = [
               "-C" "target-feature=+crt-static"
-              "-C" "link-arg=-static"
+
+              # -latomic is required to build openssl-sys for armv6l-linux, but
+              # it doesn't seem to hurt any other builds.
+              "-C" "link-args=-static -latomic"
 
               # https://github.com/rust-lang/cargo/issues/4133
               "-C" "linker=${TARGET_CC}"