GNU: Remove non-functional code in OBJCXX support

In commit 9e66397c28 (Languages: Add support for Objective-C++,
2019-09-13, v3.16.0-rc1~44^2~2) we set `CMAKE_OBCXX_LINK_FLAGS`.
It was a typo for `CMAKE_OBJCXX_LINK_FLAGS`, and so has not had
any effect.
1 file changed