use egdb (gdb from ports)

Index: src/etc/rust-gdb
--- src/etc/rust-gdb.orig
+++ src/etc/rust-gdb
@@ -19,7 +19,7 @@ RUSTC_COMMIT_HASH="$("$RUSTC" -vV | sed -n 's/commit-h
 # Run GDB with the additional arguments that load the pretty printers
 # Set the environment variable `RUST_GDB` to overwrite the call to a
 # different/specific command (defaults to `gdb`).
-RUST_GDB="${RUST_GDB:-gdb}"
+RUST_GDB="${RUST_GDB:-egdb}"
 PYTHONPATH="$PYTHONPATH:$GDB_PYTHON_MODULE_DIRECTORY" exec ${RUST_GDB} \
   --directory="$GDB_PYTHON_MODULE_DIRECTORY" \
   -iex "add-auto-load-safe-path $GDB_PYTHON_MODULE_DIRECTORY" \