So far, mimalloc does not override the `nothrow` variants of the
`delete` operator because it assumes that their implementation in the
C++ standard library redirects to the default `delete` operators. This
is not the case for GNU libstdc++ < 9, where `std::free()` is called
directly.
This issue might be the cause for the crashes reported in #261.
Upstream bug: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68210
This commit ensures that the `nothrow` `delete` operators are properly
overridden by mimalloc.
096b9015dc