Ports: Only do build check for configure, build, and install steps

This was breaking ports linting, which runs the script with the
'showproperty' option. This check is not needed for some other options
as well, so let's do it conditionally.

Ports/.port_include.sh

@@ -50,15 +50,6 @@ host_env() {
  enable_ccache
 }
 
-# Sanity check.
-if [ ! -f "${DESTDIR}/usr/lib/libc.so" ]; then
- echo "libc.so could not be found. This likely means that SerenityOS:"
- echo "- has not been built and/or installed yet"
- echo "- has been installed in an unexpected location"
- echo "The currently configured build directory is ${SERENITY_BUILD_DIR}. Resolve this issue and try again."
- exit 1
-fi
-
 packagesdb="${DESTDIR}/usr/Ports/packages.db"
 
 . "$@"
@@ -83,13 +74,27 @@ run_nocd() {
  echo "+ $@ (nocd)"
  ("$@")
 }
+
 run() {
  echo "+ $@"
  (cd "$workdir" && "$@")
 }
+
 run_replace_in_file() {
  run perl -p -i -e "$1" $2
 }
+
+ensure_build() {
+ # Sanity check.
+ if [ ! -f "${DESTDIR}/usr/lib/libc.so" ]; then
+ echo "libc.so could not be found. This likely means that SerenityOS:"
+ echo "- has not been built and/or installed yet"
+ echo "- has been installed in an unexpected location"
+ echo "The currently configured build directory is ${SERENITY_BUILD_DIR}. Resolve this issue and try again."
+ exit 1
+ fi
+}
+
 install_launcher() {
  if [ -z "$launcher_name" ] || [ -z "${launcher_category}" ] || [ -z "${launcher_command}" ]; then
  return
@@ -374,6 +379,7 @@ do_patch() {
  patch_internal
 }
 do_configure() {
+ ensure_build
  if [ "$useconfigure" = "true" ]; then
  echo "Configuring $port!"
  pre_configure
@@ -384,10 +390,12 @@ do_configure() {
  fi
 }
 do_build() {
+ ensure_build
  echo "Building $port!"
  build
 }
 do_install() {
+ ensure_build
  echo "Installing $port!"
  install
  post_install