[CMake] Make sure that assert() is disabled for any non-Debug build.
[CMake] Make sure that assert() is disabled for any non-Debug build.

This is intended to cover the case where a packager builds with an
undefined build type in order to have all compiler flags drawn from the
environment.

mwtoews/libgeos,libgeos/libgeos,libgeos/libgeos,libgeos/libgeos,libgeos/libgeos,mwtoews/libgeos,mwtoews/libgeos,libgeos/libgeos,mwtoews/libgeos,mwtoews/libgeos,mwtoews/libgeos,mwtoews/libgeos