[clang] [clang-tools-extra] [clangd] Update clangDaemonTweaks to set symbol visibility macros (PR #112304)

[Saleem Abdulrasool via cfe-commits]

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@@ -47,7 +47,7 @@ endmacro()
 
 macro(add_clang_library name)
   cmake_parse_arguments(ARG
-    "SHARED;STATIC;INSTALL_WITH_TOOLCHAIN"
+    "SHARED;STATIC;INSTALL_WITH_TOOLCHAIN;CLANG_IMPORT"
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compnerd wrote:

We should document the option. Why is it specific to clang? I think that the right semantics are, is this library built as a static library or not. The default should be dynamic. At that point, when the library is built as static, a public definition could be added at the library definition to state it is static. That would then implicitly avoid the DLL storage. Otherwise, it is implicitly DLL imported.

```c
#if defined(clang_STATIC)
# define CLANG_ABI
#else
# if defined(_WIN32)
#   if defined(clang_EXPORTS)
#     define CLANG_ABI __declspec(dllexport)
#   else
#     define CLANG_ABI __declspec(dllimport)
#   endif
# else
...
# endif
```

We don't need all this new custom handling to be wired through out the build to support this. Each library needs only to know its ABI, and in the case that it's a compacted library (i.e. is an object library), we update the export symbol that CMake uses to the DLL that it is compacted into.

Am I missing something in this model?

https://github.com/llvm/llvm-project/pull/112304