thunderbird: Add gpg/gpgme dependencies. Fixes #98765.

This enables to configure Thunderbird to use gnupg directly, which is the
official upstream recommendation when using GPG with smartcards, which are not
yet supported by Thunderbird's native GPG support.

pkgs/applications/networking/mailreaders/thunderbird/default.nix

@@ -15,6 +15,8 @@
 , glib
 , gnugrep
 , gnused
+, gnupg
+, gpgme
 , icu
 , jemalloc
 , lib
@@ -288,6 +290,15 @@ stdenv.mkDerivation rec {
     rm -rf $out/include $out/lib/thunderbird-devel-* $out/share/idl
   '';
 
+  # Note on GPG support:
+  # Thunderbird's native GPG support does not yet support smartcards.
+  # The official upstream recommendation is to configure fall back to gnupg
+  # using the Thunderbird config `mail.openpgp.allow_external_gnupg`
+  # and GPG keys set up; instructions with pictures at:
+  # https://anweshadas.in/how-to-use-yubikey-or-any-gpg-smartcard-in-thunderbird-78/
+  # For that to work out of the box, it requires `gnupg` on PATH and
+  # `gpgme` in `LD_LIBRARY_PATH`; we do this below.
+
   preFixup = ''
     # Needed to find Mozilla runtime
     gappsWrapperArgs+=(
@@ -297,6 +308,8 @@ stdenv.mkDerivation rec {
       --set SNAP_NAME "thunderbird"
       --set MOZ_LEGACY_PROFILES 1
       --set MOZ_ALLOW_DOWNGRADE 1
+      --prefix PATH : "${lib.getBin gnupg}/bin"
+      --prefix LD_LIBRARY_PATH : "${lib.getLib gpgme}/lib"
     )
   '';