fix(scripts): modify logic for determining terraform arch (#9595)

Commit fb3616c used a build-arg to set the desired terrafomr
architeture to fetch. This is set in build_docker.sh but not
when building using depot.dev. Baking the logic into the
Dockerfile instead.

scripts/Dockerfile.base

@@ -25,13 +25,11 @@ RUN apk add --no-cache \
 # Terraform was disabled in the edge repo due to a build issue.
 # https://gitlab.alpinelinux.org/alpine/aports/-/commit/f3e263d94cfac02d594bef83790c280e045eba35
 # Using wget for now. Note that busybox unzip doesn't support streaming.
-ARG ARCH
-RUN wget -O /tmp/terraform.zip "https://releases.hashicorp.com/terraform/1.5.6/terraform_1.5.6_linux_${ARCH}.zip" && \
+RUN ARCH="$(arch)"; if [ "${ARCH}" == "x86_64" ]; then ARCH="amd64"; fi; wget -O /tmp/terraform.zip "https://releases.hashicorp.com/terraform/1.5.6/terraform_1.5.6_linux_${ARCH}.zip" && \
 		busybox unzip /tmp/terraform.zip -d /usr/local/bin && \
 		rm -f /tmp/terraform.zip && \
 		chmod +x /usr/local/bin/terraform && \
 		terraform --version
-
 USER 1000:1000
 ENV HOME=/home/coder
 ENV PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/opt

scripts/build_docker.sh

@@ -103,7 +103,6 @@ declare -A arch_map=(
 	[arm]="linux/arm/v7"
 	[armv7]="linux/arm/v7"
 )
-orig_arch="$arch"
 if [[ "${arch_map[$arch]+exists}" != "" ]]; then
 	arch="${arch_map[$arch]}"
 fi
@@ -125,7 +124,6 @@ if [[ "$build_base" != "" ]]; then
 	log "--- Building base Docker image for $arch ($build_base)"
 	docker build \
 		--platform "$arch" \
-		--build-arg "ARCH=${orig_arch}" \
 		--tag "$build_base" \
 		--no-cache \
 		-f Dockerfile.base \