[llvm] [msan] Enable msan-handle-asm-conservative for userspace by default (PR #79251)

[Fangrui Song via llvm-commits]

MaskRay wrote:

> LGTM, we shouldn't enable something with potential false-negatives by default.

The false negative only occurs when the inline asm doesn't actually initialize the indirect output (`=m`). I think it is an obvious user fault :)

The opposite (false positives), which we current have for userspace msan, is worse:)

https://github.com/llvm/llvm-project/pull/79251