[clang] [Clang] Introduce __builtin_is_modifiable_lvalue() (PR #132524)

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+// RUN: %clang_cc1 -triple x86_64-pc-linux-gnu -emit-llvm < %s| FileCheck %s
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+void report(int value);
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Sirraide wrote:

Yeah, all of these should just be sema tests using `static_assert`; maybe 1 or 2 codegen tests just to make sure we can emit it at all would be nice, but that’s it imo.

https://github.com/llvm/llvm-project/pull/132524