Build lldb-mi

Building this tool requires having a full LLVM build available;
either by installing without LLVM_INSTALL_TOOLCHAIN_ONLY (and not
stripping the llvm installation yet) or by pointing it at the
LLVM build directory instead. The latter works better for our
normal build flows.

Dockerfile.cross

@@ -20,6 +20,10 @@ ARG FULL_LLVM
 
 COPY build-llvm.sh .
 RUN ./build-llvm.sh $CROSS_TOOLCHAIN_PREFIX --host=$HOST
+
+COPY build-lldb-mi.sh .
+RUN ./build-lldb-mi.sh $CROSS_TOOLCHAIN_PREFIX --host=$HOST
+
 COPY strip-llvm.sh .
 RUN ./strip-llvm.sh $CROSS_TOOLCHAIN_PREFIX --host=$HOST