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