[llvm] Sketch of build and code changes for llvm shared library build using explicit visibility annotations (PR #96630)

[Thomas Fransham via llvm-commits]

fsfod wrote:

 I've added cmake config option(LLVM_BUILD_LLVM_DYLIB_VIS) to test explicit visibility macros on windows and Linux. 
When its off the macros are nop on windows and for Linux there is no difference with it off , except the default symbol visibility is not set to hidden for llvm components.
If option is enabled llvm shared library should build on both windows(only clang-cl this early on) and Linux with it on, but tools won't link successfully yet because only limited number of symbols are exported.

https://github.com/llvm/llvm-project/pull/96630