tools: don't gitignore base64 config.h

The file is checked into git. Ignoring it causes a very non-obvious way
of breaking tarball builds:

1. Download and unpack tarball
2. Check the sources into git with `git init; git add .; git commit -a`
3. Clean the source tree with `git clean -dfx`
4. Run `./configure && make`
5. Observe build failure because config.h is missing

Fixes: #47638

Author: bnoordhuis

tools/dep_updaters/update-base64.sh

@@ -51,6 +51,10 @@ mv "$WORKSPACE/base64" "$DEPS_DIR/base64/"
 # to work, we create it and leave it empty.
 echo "// Intentionally empty" >> "$DEPS_DIR/base64/base64/lib/config.h"
 
+# Clear out .gitignore, otherwise config.h is ignored. That's dangerous when
+# people check in our tarballs into source control and run `git clean`.
+echo "# Intentionally empty" >> "$DEPS_DIR/base64/base64/.gitignore"
+
 echo "All done!"
 echo ""
 echo "Please git add base64/base64, commit the new version:"