Allow regular builds and ARM64 builds through POSIX shell

buildx sets the env var if we specify it.  Regular docker build doesn't seem to
do so.  This solution is not pretty but it tackles the cases we're trying to
support now.  Perhaps this will make Apple happy.

Author: madnificent

Dockerfile

@@ -3,12 +3,16 @@ FROM node:20-bookworm
 LABEL maintainer="team@semantic.works"
 
 RUN apt-get update && apt-get -y upgrade && apt-get -y install git openssh-client rsync jq
-RUN if [[ "$TARGETPLATFORM" -eq "linux/amd64" ]]; then \
-    cd /tmp/ && wget https://github.com/watchexec/watchexec/releases/download/v2.3.2/watchexec-2.3.2-x86_64-unknown-linux-gnu.deb && dpkg -i watchexec-2.3.2-x86_64-unknown-linux-gnu.deb; \
-    elif [[ "$TARGETPLATFORM" -eq "linux/arm64" ]]; then \
-    cd /tmp/ && wget https://github.com/watchexec/watchexec/releases/download/v2.3.2/watchexec-2.3.2-aarch64-unknown-linux-gnu.deb && dpkg -i watchexec-2.3.2-aarch64-unknown-linux-gnu.deb; \
+ARG TARGETPLATFORM
+RUN if [ "$TARGETPLATFORM" = "linux/amd64" ]; then \
+      echo "BUILDING FOR AMD64 through $TARGETPLATFORM"; cd /tmp/ && wget https://github.com/watchexec/watchexec/releases/download/v2.3.2/watchexec-2.3.2-x86_64-unknown-linux-gnu.deb && dpkg -i watchexec-2.3.2-x86_64-unknown-linux-gnu.deb; \
+    elif [ "$TARGETPLATFORM" = "linux/arm64" ]; then \
+      echo "BUILDING FOR ARM64" && cd /tmp/ && wget https://github.com/watchexec/watchexec/releases/download/v2.3.2/watchexec-2.3.2-aarch64-unknown-linux-gnu.deb && dpkg -i watchexec-2.3.2-aarch64-unknown-linux-gnu.deb; \
+    elif [ "$TARGETPLATFORM" = "" ]; then \
+      echo "BUILDING FOR AMD64 through $TARGETPLATFORM"; cd /tmp/ && wget https://github.com/watchexec/watchexec/releases/download/v2.3.2/watchexec-2.3.2-x86_64-unknown-linux-gnu.deb && dpkg -i watchexec-2.3.2-x86_64-unknown-linux-gnu.deb; \
     else \
-    echo "$TARGETPLATFORM not supported, check watchexec" ; \
+      echo "Target platform \"$TARGETPLATFORM\" not supported, check watchexec" ; \
+      exit 1; \
     fi
 
 ENV MU_SPARQL_ENDPOINT='http://database:8890/sparql'