Similar to other CI infra changes we've made recently. Move to LLVM/Clang 16 for the MSAN jobs (which is currently using LLVM 12).
See also: https://releases.llvm.org/16.0.0/tools/clang/docs/ReleaseNotes.html#sanitizers:
-fsanitize-memory-param-retvalis turned on by default. With-fsanitize=memory, passing uninitialized variables to functions and returning uninitialized variables from functions is more aggressively reported.-fno-sanitize-memory-param-retvalrestores the previous behavior.