xbps-src: detect musl hosts correctly in 'binary-bootstrap'.

xbps-src

@@ -257,8 +257,10 @@ check_build_requirements() {
 
 install_bbootstrap() {
     [ -n "$CHROOT_READY" ] && return
-    if [ -n "$1" ]; then
+    if [ "$1" = "bootstrap" ]; then
         unset XBPS_TARGET_PKG XBPS_INSTALL_ARGS
+    else
+        XBPS_TARGET_PKG="$1"
     fi
     if [ -n "$XBPS_SKIP_REMOTEREPOS" ]; then
         unset XBPS_INSTALL_ARGS
@@ -571,7 +573,7 @@ fi
 #
 case "$XBPS_TARGET" in
     binary-bootstrap)
-        install_bbootstrap
+        install_bbootstrap ${XBPS_TARGET_PKG:=$XBPS_MACHINE}
         ;;
     bootstrap)
         # bootstrap from sources