Mention $TOOLCHAIN in install_airlock help text, and accept CSV too.

scripts/help.txt

@@ -12,8 +12,8 @@
                     to show all failures.
   clean           - Delete temporary files.
   distclean       - Delete everything that isn't shipped.
-  install_airlock - Install toybox and host toolchain into $PREFIX directory
-                    (providing $PATH for hermetic builds).
+  install_airlock - Install toybox and host toolchain (plus $TOOLCHAIN if any)
+                    into $PREFIX directory, providing $PATH for hermetic builds.
   install_flat    - Install toybox into $PREFIX directory.
   install         - Install toybox into subdirectories of $PREFIX.
   uninstall_flat  - Remove toybox from $PREFIX directory.

scripts/install.sh

@@ -106,7 +106,7 @@ done
 # For now symlink the host version. This list must go away by 1.0.
 
 PENDING="expr git tr bash sh gzip   awk bison flex make ar"
-TOOLCHAIN+=" as cc ld objdump  bc gcc"
+TOOLCHAIN="${TOOLCHAIN//,/ } as cc ld objdump  bc gcc"
 
 # Tools needed to build packages
 for i in $TOOLCHAIN $PENDING $HOST_EXTRA