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

[via cfe-commits]

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@@ -6612,6 +6612,8 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
   Args.AddLastArg(CmdArgs, options::OPT_fconstexpr_depth_EQ);
   Args.AddLastArg(CmdArgs, options::OPT_fconstexpr_steps_EQ);
 
+  Args.AddLastArg(CmdArgs, options::OPT_fimplicit_constexpr);
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Sirraide wrote:

We should issue a driver diagnostic *somewhere* if someone tries to pass `-fimplicit-constexpr` if we’re not compiling C++. And we’d need tests for that too then.

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