Makefile & Cross.toml hack to work around an aarch64 cross-compilation issue (https://github.com/rust-embedded/cross/issues/598)

Cross.toml

@@ -0,0 +1,6 @@
+[build.env]
+# Both of these are needed to workaround https://github.com/rust-embedded/cross/issues/598
+passthrough = [
+    "RUSTFLAGS",
+    "CARGO_TARGET_AARCH64_UNKNOWN_LINUX_MUSL_RUSTFLAGS",
+]

Makefile

@@ -64,10 +64,15 @@ arm-binary-release:
 arm-binary-debug:
 	cross build --target=armv7-unknown-linux-musleabihf --all-targets --features vendored-openssl
 
+# Hack to workaround https://github.com/rust-embedded/cross/issues/598
+HACK_WORKAROUND_ISSUE_598=CARGO_TARGET_AARCH64_UNKNOWN_LINUX_MUSL_RUSTFLAGS="-C link-arg=/usr/local/aarch64-linux-musl/lib/libc.a"
+
 aarch64-binary: aarch64-binary-release
 
 aarch64-binary-release:
-	cross build --target=aarch64-unknown-linux-musl --release --all-targets --features vendored-openssl
+	$(HACK_WORKAROUND_ISSUE_598) \
+		cross build --target=aarch64-unknown-linux-musl --release --all-targets --features vendored-openssl
 
 aarch64-binary-debug:
-	cross build --target=aarch64-unknown-linux-musl --all-targets --features vendored-openssl
+	$(HACK_WORKAROUND_ISSUE_598) \
+		cross build --target=aarch64-unknown-linux-musl --all-targets --features vendored-openssl