implement more robust detection of sized delete support

As reported in issue #954, osx clang compiler is able to optimize our
previous detection away while not really having runtime support for
sized delete. So this time we use AC_LINK_IFELSE and more robust code
to prevent compiler from optimizing away sized delete call. This
should reliably catch "bad" compilers.

Special thanks to Alexey Serbin for reporting the issue, suggesting a
fix and verifying it.

Fixes issue #954.
1 file changed