Fixup builders 0100

Author: webmaster128

builders/Dockerfile.alpine

@@ -1,4 +1,4 @@
-FROM rust:1.77.0-alpine
+FROM --platform=linux/amd64 rust:1.77.0-alpine
 
 RUN apk add --no-cache ca-certificates build-base
 

builders/Dockerfile.cross

@@ -1,4 +1,4 @@
-FROM rust:1.77.0-bullseye
+FROM --platform=linux/amd64 rust:1.77.0-bullseye
 
 # Install build dependencies
 RUN apt-get update \

builders/README.md

@@ -28,6 +28,7 @@ See those DockerHub repos for all available versions of the builder images.
 - Rename builder image from cosmwasm/go-ext-builder to
   cosmwasm/libwasmvm-builder
 - Replace CentOS with Debian image for GNU linux builds
+- Build all images with `--platform=linux/amd64` to avoid accidental ARM builds
 
 **Version 0019:**
 
@@ -131,8 +132,9 @@ See those DockerHub repos for all available versions of the builder images.
 
 ## Usage
 
-Create a local docker image, capable of cross-compling linux and macos dynamic
-libs:
+Create the Docker images, capable of cross-compling Linux and MacOS dynamic
+libs. As the builder images are all x86_64, it can be slow and memory intense to
+do this on a different architecture:
 
 ```sh
 (cd builders && make docker-images)