Ports: Don't set previously unset environment variables

Co-authored-by: Tim Schumacher <timschumi@gmx.de>
Co-authored-by: Jelle Raaijmakers <jelle@gmta.nl>

Ports/.strip_env.sh

@@ -1,13 +1,27 @@
 #!/usr/bin/env bash
 
-exec env -i SERENITY_STRIPPED_ENV=1 \
-    HOME="${HOME}" \
-    USER="${USER}" \
-    TERM="${TERM}" \
-    PATH="${PATH}" \
-    EDITOR="${EDITOR:-}" \
-    MAKEJOBS="${MAKEJOBS:-}" \
-    IN_SERENITY_PORT_DEV="${IN_SERENITY_PORT_DEV:-}" \
-    SERENITY_ARCH="${SERENITY_ARCH:-}" \
-    SERENITY_TOOLCHAIN="${SERENITY_TOOLCHAIN:-}" \
-    "${@}"
+environment_variables=(
+    "HOME=${HOME}"
+    "PATH=${PATH}"
+    "SERENITY_STRIPPED_ENV=1"
+    "TERM=${TERM}"
+    "USER=${USER}"  
+)
+
+# If any of the following optional variables are set, keep them.
+keep_environment_variables=(
+    'EDITOR'
+    'IN_SERENITY_PORT_DEV'
+    'MAKEJOBS'
+    'SERENITY_ARCH'
+    'SERENITY_TOOLCHAIN'
+    'VISUAL'
+)
+
+for environment_variable_name in "${keep_environment_variables[@]}"; do
+    if [ -v "${environment_variable_name}" ]; then
+        environment_variables+=("${environment_variable_name}=${!environment_variable_name}")
+    fi
+done
+
+exec env -i "${environment_variables[@]}" "${@}"