Suppress some noisy / buggy warnings (#1136)
Two warnings were being emitted in the MSVC+LLVM tests.
The warning `-Wunsafe-buffer-usage` is initially introduced in some capacity here https://reviews.llvm.org/
D137346 pointing to documentation at https://discourse.llvm.org/t/rfc-c-buffer-hardening/65734. The warning is a stylistic checker whose goal is to "emit a warning every time an unsafe operation is performed on a raw pointer". This type of programming model is not useful for library implementations of types such as `span`, where direct manipulation of raw pointers is inevitable, so disable the warning altogether.
There is also a false-positive warning https://github.com/llvm/llvm-project/issues/65689 that I've disabled inline.