Prepare libcxx and libcxxabi for pointer field protection.
Pointer field protection has the following characteristics:
- Pointer fields in RTTI types are unsigned. Signing these fields
is unnecessary because PFP is a mechanism for protecting the heap,
and the RTTI objects typically live in global variables. Therefore,
mark the fields with the no_field_protection to inhibit PFP for these
fields.
- libcxx's interim trivial relocatability implementation, which memcpy's
some non-trivially-copyable objects according to the value of a trait,
conflicts with PFP in tagged mode (in which the address of the pointer
is used as part of the pointer encoding) by causing such copies to
result in a crash in some cases where the object being copied includes
a pointer field. These copies are undefined behavior. Therefore, make
libcxx's trivially relocatable predicate simply return the value of
the trivially copyable trait when PFP in tagged mode is enabled, which
results in standards compliant behavior that is accommodated by PFP.
Reviewers: philnik777, fmayer, ldionne
Pull Request: https://github.com/llvm/llvm-project/pull/151651
