Strip the llvm installation after building

This still inflates the docker image chain since it's done in
a separate RUN command though.

This tests that one still can (re)build
compiler-rt/libunwind/libcxxabi/libcxx after stripping down the llvm
installation.

Dockerfile.dev

@@ -21,6 +21,12 @@ ENV TOOLCHAIN_PREFIX=/opt/llvm-mingw
 COPY build-llvm.sh .
 RUN ./build-llvm.sh $TOOLCHAIN_PREFIX
 
+# Strip the LLVM install output immediately. (This doesn't reduce the
+# total docker image size as long as it is in a separate RUN layer though,
+# but reduces build times if tweaking the contents of strip-llvm.sh.)
+COPY strip-llvm.sh .
+RUN ./strip-llvm.sh $TOOLCHAIN_PREFIX
+
 ENV TOOLCHAIN_ARCHS="i686 x86_64 armv7 aarch64"
 
 # Install the usual $TUPLE-clang binaries
@@ -70,11 +76,6 @@ RUN cd test && \
 COPY build-libssp.sh libssp-Makefile ./
 RUN ./build-libssp.sh $TOOLCHAIN_PREFIX
 
-# Strip the final toolchain. (This doesn't reduce the total docker image
-# size as long as it is in a separate RUN layer though.)
-COPY strip-llvm.sh .
-RUN ./strip-llvm.sh $TOOLCHAIN_PREFIX
-
 # Cheating: Pull strip and objcopy from the normal binutils package.
 RUN apt-get update -qq && \
     apt-get install -qqy binutils-mingw-w64-x86-64 && \