Enable libc++ and LLVM pretty printers for gdb (#4715)

.gdbinit

@@ -2,5 +2,6 @@
 # Exceptions. See /LICENSE for license information.
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-source third_party/llvm-project/libcxx/utils/gdb/libcxx/printers.py
+source external/_main~llvm_project~llvm-project/llvm/utils/gdb-scripts/prettyprinters.py
+source external/_main~llvm_project~llvm-project/libcxx/utils/gdb/libcxx/printers.py
 python register_libcxx_printer_loader()