[clang] [Clang][AST] fix crash in mangle lambda expression (PR #78896)

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cor3ntin wrote:

both compiler seems to mangkle it as `_ZNK6XXXYYYMUlT_E_clIiEEDaS0_` which looks correct
(`auto XXXYYY::{lambda(auto:1)#1}::operator()<int>(int) const`) @rjmccall 

Compiler explorer let you demangle identifiers (in the output menu, under the compilers dropdown https://compiler-explorer.com/z/Th11TjM8K )

https://github.com/llvm/llvm-project/pull/78896