Use piwheels for armv7 docker image builds (#5703)

docker/Dockerfile

@@ -14,6 +14,7 @@ FROM base-${BASEIMGTYPE} AS base
 
 ARG TARGETARCH
 ARG TARGETVARIANT
+ARG PIP_EXTRA_INDEX_URL
 
 # Note that --break-system-packages is used below because
 # https://peps.python.org/pep-0668/ added a safety check that prevents
@@ -46,7 +47,7 @@ RUN \
           libssl-dev=3.0.11-1~deb12u2 \
           libffi-dev=3.4.4-1 \
           cargo=0.66.0+ds1-1 \
-          pkg-config=1.8.1-1; \
+          pkg-config=1.8.1-1 \
           gcc-arm-linux-gnueabihf=4:12.2.0-3; \
     fi; \
     rm -rf \
@@ -58,8 +59,8 @@ ENV \
   # Fix click python3 lang warning https://click.palletsprojects.com/en/7.x/python3/
   LANG=C.UTF-8 LC_ALL=C.UTF-8 \
   # Store globally installed pio libs in /piolibs
-  PLATFORMIO_GLOBALLIB_DIR=/piolibs
-
+  PLATFORMIO_GLOBALLIB_DIR=/piolibs \
+  PIP_EXTRA_INDEX_URL=${PIP_EXTRA_INDEX_URL}
 
 # Support legacy binaries on Debian multiarch system. There is no "correct" way
 # to do this, other than using properly built toolchains...

docker/build.py

@@ -143,15 +143,25 @@ def main():
         imgs = [f"{params.build_to}:{tag}" for tag in tags_to_push]
         imgs += [f"ghcr.io/{params.build_to}:{tag}" for tag in tags_to_push]
 
+        build_args = [
+            "--build-arg",
+            f"BASEIMGTYPE={params.baseimgtype}",
+            "--build-arg",
+            f"BUILD_VERSION={args.tag}",
+        ]
+
+        if args.arch == ARCH_ARMV7:
+            build_args += [
+                "--build-arg",
+                "PIP_EXTRA_INDEX_URL=https://www.piwheels.org/simple",
+            ]
+
         # 3. build
         cmd = [
             "docker",
             "buildx",
             "build",
-            "--build-arg",
-            f"BASEIMGTYPE={params.baseimgtype}",
-            "--build-arg",
-            f"BUILD_VERSION={args.tag}",
+            *build_args,
             "--cache-from",
             f"type=registry,ref={cache_img}",
             "--file",