Factor out architecture map

lib.sh.in

@@ -149,6 +149,14 @@ register_binfmt() {
     # kernel select an alternate interpreter.  More values for this
     # map can be obtained from here:
     # https://github.com/qemu/qemu/blob/master/scripts/qemu-binfmt-conf.sh
+
+    # If the XBPS_TARGET_ARCH is unset but the PLATFORM is known, it
+    # may be possible to set the architecture from the static
+    # platforms map.
+    if [ -z "$XBPS_TARGET_ARCH" ] && [ ! -z "$PLATFORM" ] ; then
+        set_target_arch_from_platform
+    fi
+
     case "${XBPS_TARGET_ARCH}" in
         armv*)
             _cpu=arm
@@ -213,6 +221,34 @@ register_binfmt() {
     fi
 }
 
+set_target_arch_from_platform() {
+    # This function maintains a lookup from platform to target
+    # architecture.  This is required for scripts that need to know
+    # the target architecture, but don't necessarily need to know it
+    # internally (i.e. only run_cmd_chroot).
+    case "$PLATFORM" in
+        bananapi*) XBPS_TARGET_ARCH="armv7l";;
+        beaglebone*) XBPS_TARGET_ARCH="armv7l";;
+        cubieboard2*|cubietruck*) XBPS_TARGET_ARCH="armv7l";;
+        dockstar*) XBPS_TARGET_ARCH="armv5tel";;
+        odroid-u2*) XBPS_TARGET_ARCH="armv7l";;
+        odroid-c2*) XBPS_TARGET_ARCH="aarch64";;
+        rpi3*) XBPS_TARGET_ARCH="aarch64";;
+        rpi2*) XBPS_TARGET_ARCH="armv7l";;
+        rpi*) XBPS_TARGET_ARCH="armv6l";;
+        usbarmory*) XBPS_TARGET_ARCH="armv7l";;
+        ci20*) XBPS_TARGET_ARCH="mipsel";;
+        i686*) XBPS_TARGET_ARCH="i686";;
+        x86_64*) XBPS_TARGET_ARCH="x86_64";;
+        GCP*) XBPS_TARGET_ARCH="x86_64";;
+        *) die "$PROGNAME: Unable to compute target architecture from platform";;
+    esac
+
+    if [ -z "${PLATFORM##*-musl}" ] ; then
+        XBPS_TARGET_ARCH="${XBPS_TARGET_ARCH}-musl"
+    fi
+}
+
 set_cachedir() {
     # The package artifacts are cacheable, but they need to be isolated
     # from the host cache.