legacysupport @1.0.4: Add support for missing "operator delete ( void* ptr, std::size_t sz )" in macos < 10.12

[tenzap]

Originally, when building KeePassXC on macOS 10.11 with a compiler that supports the -fsized-deallocation (like clang++-mp-9.0, or a recent AppleClang, probably >= 8) there is this error:

error: call to unavailable function 'operator delete': introduced in macOS 10.12

Test case file to compile with -fsized-deallocation flag:

#include <new>
int main() {
  void * ptr = nullptr;
  std::size_t size = 1;
  ::operator delete(ptr, size);
}

Maybe this is part of the things that could be added to legacysupport?

For now this is worked around in KeePassXC with a patch that disables use of -fsized-deallocation on macos < 10.12.