https://github.com/dlang/dmd/pull/17044
It's enabled with -preview=safer
It enables "safe by default". This is different from marking functions as @safe,
in that:
1. it does not mark the function as @safe, the function mangling does not change
2. it enables all @safe checks except it does not complain about calling @system
functions
3. it does not interfere with attribute inference
In other words, it does not impose transitive safety. You can still call
malloc() and printf() in it.
Once it appears in the next release, I encourage people to add -preview=safer to
their build process.
