[clang] [clang] add `-fimplicit-constexpr` flag (PR #136436)

[Hana Dusíková via cfe-commits]

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@@ -0,0 +1,51 @@
+// RUN: %clang_cc1 -verify=normal,both -std=c++23 %s
+// RUN: %clang_cc1 -verify=implicit,both -fimplicit-constexpr -std=c++23 %s
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hanickadot wrote:

new test added for earlier standards too

https://github.com/llvm/llvm-project/pull/136436