mail/thunderbird: fix build with clang 19

clang/libcxx 19 is more strict about std::char_traits, causing build
failure in the rnp submodule. Import patches from upstream (rnp).

PR: 282347
Submitted by: jkim@

(cherry picked from commit 74e2551e863ba50a34faeeec03b82a078e8cb8e2)