[compiler-rt] Fix an MSVC build issue. (PR #111557)

[Martin Storsjö via llvm-commits]

mstorsjo wrote:

> Silently skipping compiling bits of compiler-rt seems bad... it seems likely to lead to a situation where a toolchain is broken in a very subtle way. These particular bits of compiler-rt probably aren't that important in most cases, but still, it seems problematic. Could you explain why you're building compiler-rt with MSVC, instead of doing the usual LLVM_ENABLE_RUNTIMES build?

I would presume that they're building compiler-rt with MSVC, for use with MSVC - primarily the sanitizers, but they're getting the builtins at the same time, even if they don't really need/use them. (AFAIK they've been shipping that in some form for years already, but probably with a number of downstream changes to get it to build in their setup - and they're now trying to get rid of the difference to upstream.)

https://github.com/llvm/llvm-project/pull/111557