[compiler-rt] [lsan] Use VReport if not REGISTERS_AVAILABLE (PR #116555)

[Vitaly Buka via llvm-commits]

vitalybuka wrote:

> Since registers as the root set aren't very useful anyway, just switch
> to VReport instead.

They are critical to avoid false leak reports, and this condition means LSAN is broken.
Thread can be suspended in any moment. A pointer to just allocated memory can be in register only.
It would be nice to understand how we get there.

https://github.com/llvm/llvm-project/pull/116555