Add $LDAI_RUNTIME_FILE

Author: TheAssassin

README.md

@@ -39,6 +39,7 @@ linuxdeploy-plugin-appimage can be configured using environment variables.
 - `LDAI_SIGN_KEY=key_id`: GPG Key ID to use for signing. This environment variable is only used if `SIGN` is set.
 - `LDAI_VERBOSE=1`: set this variable to any value to enable verbose output
 - `LDAI_OUTPUT=filename`: change filename of resulting AppImage
+- `LDAI_RUNTIME_FILE`: path to custom AppImage runtime appimagetool should use
 - `LDAI_NO_APPSTREAM=1`: skip checking AppStream metadata for issues
 - `LDAI_APPIMAGE_COMP=...`: compression algorithm appimagetool/mksquashfs should use (e.g., `xz`, `gzip`), see [appimagetool's repository](https://github.com/AppImage/AppImageKit/) for more information
 - `LINUXDEPLOY_OUTPUT_APP_NAME`: sets `APPIMAGETOOL_APP_NAME` to configure appimagetool's autogenerated filename prefix

src/main.cpp

@@ -183,6 +183,11 @@ int main(const int argc, const char* const* const argv) {
         args.push_back(strdup(value.c_str()));
     });
 
+    doSomethingWithEnvVar({"LDAI_RUNTIME_FILE"}, [&](const auto& value) {
+        args.push_back(strdup("--runtime-file"));
+        args.push_back(strdup(value.c_str()));
+    });
+
     doSomethingWithEnvVar({"LDAI_NO_APPSTREAM", "NO_APPSTREAM"}, [&](const auto& value) {
         (void) value;
         args.push_back(strdup("--no-appstream"));