[clang] [clang][bytecode] Use tailcalls via `[[clang::musttail]]` (PR #173756)

[Timm Baeder via cfe-commits]

tbaederr wrote:

Why does the `has_cpp_attribute` check work if the calling convention is not supported?
Anyway, I incorporated that into https://github.com/llvm/llvm-project/pull/188419, thanks.

https://github.com/llvm/llvm-project/pull/173756