Change array to string because we're using 'set -u'.

In bash 4.3 and below, empty arrays and 'set -u' are incompatible.

OSH now builds on OS X!

build/compile.sh

@@ -171,7 +171,7 @@ build() {

  pushd $PY27

  local -a readline_flags
  local readline_flags=''
  if [[ "$HAVE_READLINE" -eq 1 ]]; then
    # Readline interface for tokenizer.c and [raw_]input() in bltinmodule.c.
    # For now, we are using raw_input() for the REPL.  TODO: Parameterize this!
@@ -180,15 +180,14 @@ build() {
    c_module_src_list=$(cat $abs_c_module_srcs)

    if [[ -n "$READLINE_DIR" ]]; then
      readline_flags+=(-L "$READLINE_DIR/lib" -I "$READLINE_DIR/include")
      readline_flags+="-L $READLINE_DIR/lib -I $READLINE_DIR/include"
    fi

    # NOTE: pyconfig.h has HAVE_LIBREADLINE but doesn't appear to use it?
    readline_flags+=(-l readline -D HAVE_READLINE)
    readline_flags+="-l readline -D HAVE_READLINE"
  else
    # don't fail
    c_module_src_list=$(grep -v '/readline.c' $abs_c_module_srcs || true)
    readline_flags=()
  fi

  # $PREFIX comes from ./configure and defaults to /usr/local.
@@ -209,7 +208,7 @@ build() {
    $c_module_src_list \
    Modules/ovm.c \
    -l m \
    "${readline_flags[@]}" \
    $readline_flags \
    "$@" \
    || true
  popd