When using Win32/x86 in a version block is that the compiler or OS?

[Gary Willoughby]

When using Win32/x86 in a version block, does that relate to the 
compiler or OS?

for example:
version(Win32)
{
    // 32bit Windows or 32bit Compiler?
}

version(X86)
{
    // 32bit OS or 32bit Compiler?
}

If these don't relate to the compiler is there any indication 
that the program is being compiled with a 32bit compiler?

I'm primarily asking because i need to use this to constrain dub 
to build different things depending on what compiler is used and 
on what architecture.