[llvm] [bazel] Correct config.h definitions for musl (PR #207295)

[Johan Euphrosine via llvm-commits]

proppy wrote:

> ASAP I will try to convert this to use https://github.com/bazel-contrib/platforms_contrib/ for these constraints instead, but I'm not sure yet how many changes that will require

@keith should we create an issue to track this? That way all the downstream project (tensorflow, xla, xls) can revert their patch once fixed upstream.

(Note: we applied  the same workaround here: https://github.com/google/xls/commit/08f280b40cc0b7ea9d7050566d4c609ca45cc0f6)

https://github.com/llvm/llvm-project/pull/207295