Try combined amd64/arm64 build

Split Dockerfile so z88dk doesn't have to be rebuilt every time it falls out od cache

.devcontainer/Dockerfile

@@ -1,5 +1,8 @@
 # syntax=docker/dockerfile:1
 
+# My current workflow is to build this on an M1 MacBook for both amd64 and arm64 using:
+# docker buildx build --platform linux/arm64/v8,linux/amd64 -t boarstone.mcphail.uk/mcphail/speccydev:tagname .
+
 FROM ubuntu:24.04 AS build
 RUN apt-get update \
 	&& apt-get install -y --no-install-recommends \
@@ -46,51 +49,6 @@ RUN cd taptools/taptools* \
 	&& make -j8 \
 	&& make install
 
-FROM ubuntu:24.04 AS z88dk
-RUN apt-get update \
-	&& apt-get install -y --no-install-recommends \
-	bison \
-	build-essential \
-	ca-certificates \
-	ccache \
-	cpanminus \
-	curl \
-	dos2unix \
-	flex \
-	gdb \
-	git \
-	libboost-all-dev \
-	libcapture-tiny-perl \
-	libclone-perl \
-	libdata-hexdump-perl \
-	libfile-slurp-perl \
-	libgmp3-dev \
-	liblocal-lib-perl \
-	libmodern-perl-perl \
-	libpath-tiny-perl \
-	libregexp-common-perl \
-	libtext-table-perl \
-	libxml2-dev \
-	libyaml-perl \
-	m4 \
-	make \
-	perl \
-	pkg-config \
-	ragel \
-	re2c \
-	texi2html \
-	texinfo \
-	zlib1g-dev \
-	&& rm -rf /var/lib/apt/lists/*
-ENV Z88DK_PATH="/opt/z88dk"
-RUN cpanm -l $HOME/perl5 --no-wget local::lib Template::Plugin::YAML \
-	&& git clone --depth 1 --branch v2.4 --recursive https://github.com/z88dk/z88dk.git ${Z88DK_PATH} \
-	&& cd ${Z88DK_PATH} \ 
-	&& eval "$(perl -I$HOME/perl5/lib/perl5 -Mlocal::lib)" \
-	&& chmod 777 build.sh \
-	&& BUILD_SDCC=1 BUILD_SDCC_HTTP=1 ./build.sh \
-	&& make install-clean bins-clean 
-
 FROM ubuntu:24.04
 RUN apt-get update \
 	&& apt-get install -y --no-install-recommends \
@@ -120,7 +78,13 @@ COPY --from=build /inpaws/inpaws /bin/inpaws
 COPY --from=build /usr/local/bin/ /usr/local/bin/
 COPY --from=build /usr/local/lib/python3.12/dist-packages/skoolkit/ /usr/local/lib/python3.12/dist-packages/skoolkit/
 COPY --from=build /opt/pasta80 /opt/pasta80
-COPY --from=z88dk /opt/z88dk/ /opt/z88dk/
+
+# z88dk takes a long time to cross compile so I'm keeping this in a separate container
+# so it doesn't require building every time the cache expires. The Dockerfile for z88dk
+# is in a subdirectory of this one. If you're building the container yourself you may
+# want to alter the next line to your own tagged build of z88dk but you're welcome to
+# use mine.
+COPY --from=boarstone.mcphail.uk/mcphail/z88dk:v2.4 /opt/z88dk/ /opt/z88dk/
 ENV PATH="${PATH}:/opt/z88dk/bin:/opt/zxbasic:/opt/zxbasic/tools:/opt/pasta80"
 ENV ZCCCFG="/opt/z88dk/lib/config"
 USER ubuntu

.devcontainer/devcontainer.json

@@ -2,7 +2,7 @@
 	"name": "ZX Spectrum dev tools",
 	//"build": { "dockerfile": "Dockerfile" },
 	// The Dockerfile takes an age to build due to z88dk, so pull from prebuilt:
-	"image": "boarstone.mcphail.uk/mcphail/speccydev:v7.0",
+	"image": "boarstone.mcphail.uk/mcphail/speccydev:combined",
 	"remoteUser": "ubuntu",
 	"runArgs": [
 		"--network=host"

.devcontainer/z88dk/Dockerfile

@@ -0,0 +1,55 @@
+# syntax=docker/dockerfile:1
+
+# Similar to the speccydev container, I'm building this with:
+# docker buildx build --platform linux/arm64/v8,linux/amd64 -t boarstone.mcphail.uk/mcphail/z88dk:tagname .
+
+FROM ubuntu:24.04 AS build
+RUN apt-get update \
+	&& apt-get install -y --no-install-recommends \
+	bison \
+	build-essential \
+	ca-certificates \
+	ccache \
+	cpanminus \
+	curl \
+	dos2unix \
+	flex \
+	gdb \
+	git \
+	libboost-all-dev \
+	libcapture-tiny-perl \
+	libclone-perl \
+	libdata-hexdump-perl \
+	libfile-slurp-perl \
+	libgmp3-dev \
+	liblocal-lib-perl \
+	libmodern-perl-perl \
+	libpath-tiny-perl \
+	libregexp-common-perl \
+	libtext-table-perl \
+	libxml2-dev \
+	libyaml-perl \
+	m4 \
+	make \
+	perl \
+	pkg-config \
+	ragel \
+	re2c \
+	texi2html \
+	texinfo \
+	zlib1g-dev \
+	&& rm -rf /var/lib/apt/lists/*
+ENV Z88DK_PATH="/opt/z88dk"
+RUN cpanm -l $HOME/perl5 --no-wget local::lib Template::Plugin::YAML \
+	&& git clone --depth 1 --branch v2.4 --recursive https://github.com/z88dk/z88dk.git ${Z88DK_PATH} \
+	&& cd ${Z88DK_PATH} \ 
+	&& eval "$(perl -I$HOME/perl5/lib/perl5 -Mlocal::lib)" \
+	&& chmod 777 build.sh \
+	&& BUILD_SDCC=1 BUILD_SDCC_HTTP=1 ./build.sh \
+	&& make install-clean bins-clean 
+
+FROM ubuntu:24.04
+COPY --from=build /opt/z88dk/ /opt/z88dk/
+ENV PATH="$(PATH):/opt/z88dk/bin"
+ENV ZCCCFG="/opt/z88dk/lib/config"
+USER ubuntu