With the acceptance of SE-0458, allow the use of unsafe expressions, the
@safe and @unsafe attributes, and the `unsafe` effect on the for..in loop
in all Swift code.
Introduce the `-strict-memory-safety` flag detailed in the proposal to
enable strict memory safety checking. This enables a new class of
feature, an optional feature (that is *not* upcoming or experimental),
and which can be detected via `hasFeature(StrictMemorySafety)`.
Extend the module trace format with a field indicating whether a given
module, or any module it depends on, was compiled with strict memory
safety enabled. This separate output from the compiler can be used as
part of an audit to determine what parts of Swift programs are built
with strict memory safety checking enabled.
