msvc currently warns about

[2879/4971] Building CXX object source\blender\draw\CMakeFiles\bf_draw.dir\intern\draw_manager_data.cc.obj
K:\BlenderGit\blender\source\blender\draw\intern\../../blenlib/intern/list_sort_impl.h(58): warning C4005: '_CONCAT': macro redefinition
k:\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.33.31629\include\xatomic.h(23): note: see previous definition of '_CONCAT'

This header hasn't changed much since it got introduced in rB867cd2048e0e: Replace linked-list insert-sort with merge-sort but i suppose it got included from some C++ code that dragged in a system header it did not drag in before.

Who's in the wrong? Clearly us, the c++ spec says globals starting with _ (lib.global.names section from the C++ spec) are reserved to the implementation, us picking something common as _CONCAT only made a collision more likely to happen.

Now I can see wanting to limit the visibility in the rest of the codebase, so i understand why we chose to make it start with an underscore, but it can't stay like this. I changed all prefixes to _BLI_xxxx , we'd still violate spec, but it be a lot less likely to collide

I would also accept spec compliant BLI_xxxx but that may risk people actually using this. which is fine, but this macro should likely not live in this header if that's the case.