[clang-tools-extra] [clang] [mlir] [llvm] [openmp] [compiler-rt] [libcxx] [lld] [flang] [libc] [lldb] [libc++][format] P2637R3: Member `visit` (`std::basic_format_arg`) (PR #76449)

[Mark de Wever via cfe-commits]

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@@ -470,4 +470,9 @@ inline Tp const& DoNotOptimize(Tp const& value) {
 #  define TEST_IF_AIX(arg_true, arg_false) arg_false
 #endif
 
+// Clang-18 has support for deducing this, but it does not set the FTM.
+#if defined(__cpp_explicit_this_parameter) || (defined(_LIBCPP_CLANG_VER) && _LIBCPP_CLANG_VER >= 1800)
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mordante wrote:

This in one of the exceptions where we can use 
```suggestion
#ifdef _LIBCPP_HAS_EXPLICIT_THIS_PARAMETER
```
MSVC STL has their own test file `libcxx/test/support/msvc_stdlib_force_include.h` where they can set this define for their compilers when they implement it.

https://github.com/llvm/llvm-project/pull/76449