Add x86_64-unknown-redox Dockerfile

Author: JohnTitor

ci/docker/x86_64-unknown-redox/Dockerfile

@@ -0,0 +1,9 @@
+FROM redoxos/redoxer
+
+RUN mv /root/.redoxer /.redoxer
+
+ENV PATH=$PATH:/.redoxer/toolchain/bin:/rust/bin \
+    AR_x86_64_unknown_redox="x86_64-unknown-redox-ar" \
+    CC_x86_64_unknown_redox="x86_64-unknown-redox-gcc" \
+    CARGO_TARGET_X86_64_UNKNOWN_REDOX_LINKER="x86_64-unknown-redox-gcc" \
+    CARGO_TARGET_X86_64_UNKNOWN_REDOX_RUNNER="redoxer exec --folder ."