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b694ada294
"POD" is the wrong type trait to determine if something can be safely
zero-filled in order to achieve zero initialization. Consider a type
like
struct POD { int POD::*ptr; };
This is a POD; its value initialization needs to value initialize the
member, and since it's a pointer, that's zero initialization, and that's
setting the pointer to null.
On Itanium, a null pointer to data member is not zero filled; it actually
has the value -1u.
Hence, zero-filling via memset(0) a POD object like the one above is
erroneous. Unfortunately there is no type trait in C++ that we can use to
know if a given datatype can be value initialized by zero-filling -- we
can check for trivial constructability, but that's a necessary
condition, not a sufficient one (POD above is also trivially
constructible).
The test is disabled on MSVC because of a compiler bug.
Fixes #238