This change adds a new weak API function which makes the sanitizer
ignore the call to free(), and implements the
functionality in ASan and HWAsan. The runtime that implements this hook
can then call free() at a later point again on the same pointer (and
making sure the hook returns zero so that the memory will actually be
freed) when it's actually ready for the memory to be cleaned up.
This is needed in order to implement an sanitizer-compatible version
of Chrome's BackupRefPtr algorithm, since process-wide double-shimming
of malloc/free does not work on some platforms.
Requested and designed by @c01db33f (Mark) from Project Zero.
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Co-authored-by: Mark Brand <markbrand@google.com>
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