[clang] [Clang] Implement P2308R1 - Template Parameter Initialization. (PR #73103)

[Aaron Ballman via cfe-commits]

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+// RUN: %clang_cc1 -std=c++98 -triple x86_64-unknown-unknown %s -verify -fexceptions -fcxx-exceptions -pedantic-errors \
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AaronBallman wrote:

I don't think we need `-fexceptions -fcxx-exceptions -Wno-variadic-macros -Wno-c11-extensions` either.

https://github.com/llvm/llvm-project/pull/73103