net-im/telegram-desktop: unbreak build on FreeBSD versions with base LLVM < 16

Minimal required LLVM version to build is 16 now.

It is stated on the clang release page, that the proposals for doing these kinds of captures are implemented in Clang16

Error example:

/wrkdirs/overlays/wip/net-im/telegram-desktop/work-qt5/tdesktop-4.14.4-full/Telegram/SourceFiles/window/window_session_controller.cpp
/wrkdirs/overlays/wip/net-im/telegram-desktop/work-qt5/tdesktop-4.14.4-full/Telegram/SourceFiles/window/window_session_controller.cpp:1249:9: error: reference to local binding 'index' declared in enclosing lambda expression

if (index >= list.size()) {
    ^

/wrkdirs/overlays/wip/net-im/telegram-desktop/work-qt5/tdesktop-4.14.4-full/Telegram/SourceFiles/window/window_session_controller.cpp:1246:29: note: 'index' declared here

for (const auto [command, index] : accounts) {
                          ^

/wrkdirs/overlays/wip/net-im/telegram-desktop/work-qt5/tdesktop-4.14.4-full/Telegram/SourceFiles/window/window_session_controller.cpp:1252:31: error: reference to local binding 'index' declared in enclosing lambda expression

const auto account = list[index];
                          ^

/wrkdirs/overlays/wip/net-im/telegram-desktop/work-qt5/tdesktop-4.14.4-full/Telegram/SourceFiles/window/window_session_controller.cpp:1246:29: note: 'index' declared here

for (const auto [command, index] : accounts) {
                          ^

2 errors generated.

Reported by: Benjamin Takacs <nimaje+fbz@bureaucracy.de>