refactor: extract build variables

Signed-off-by: Martin Kröning <[email protected]>

Dockerfile

@@ -1,3 +1,6 @@
+ARG TARGET=x86_64-hermit
+ARG PREFIX=/opt/hermit
+
 FROM --platform=$BUILDPLATFORM rust:bookworm AS kernel
 ADD --link https://github.com/hermit-os/kernel.git#hermit-c /kernel
 WORKDIR /kernel
@@ -32,10 +35,13 @@ ADD --link https://github.com/hermit-os/newlib.git newlib
 ADD --link https://github.com/hermit-os/pthread-embedded.git pte
 ADD --link ./toolchain.sh ./toolchain.sh
 
-RUN ./toolchain.sh x86_64-hermit /opt/hermit
+ARG TARGET
+ARG PREFIX
+RUN ./toolchain.sh ${TARGET} ${PREFIX}
 
 
 FROM rust:bookworm AS toolchain
-COPY --from=builder /opt/hermit /opt/hermit
-ENV PATH=/opt/hermit/bin:$PATH \
-    LD_LIBRARY_PATH=/opt/hermit/lib:$LD_LIBRARY_PATH
+ARG PREFIX
+COPY --from=builder ${PREFIX} ${PREFIX}
+ENV PATH=${PREFIX}/bin:$PATH \
+    LD_LIBRARY_PATH=${PREFIX}/lib:$LD_LIBRARY_PATH