This avoids trying to preload the 32-bit library into 64-bit processes.
The exception is ctest which will be tried, but it's easiest to do it this way.
gcov 8 outputs **a lot** (gigabytes) of messages like
```
test_tile_elements.dir/test/tests/TestData.cpp.gcno:'main' has arcs to entry block
test_tile_elements.dir/test/tests/TestData.cpp.gcno:'main' has arcs from exit block
test_tile_elements.dir/test/tests/TileElements.cpp.gcno:'main' has arcs to entry block
test_tile_elements.dir/test/tests/TileElements.cpp.gcno:'main' has arcs from exit block
test_tile_elements.dir/test/tests/TileElements.cpp.gcno:'_ZNK9__gnu_cxx13new_allocatorIcE8max_sizeEv' has arcs to entry block
test_tile_elements.dir/test/tests/TileElements.cpp.gcno:'_ZNK9__gnu_cxx13new_allocatorIcE8max_sizeEv' has arcs from exit block
test_tile_elements.dir/test/tests/TileElements.cpp.gcno:'_ZN9__gnu_cxx13new_allocatorIcE8allocateEjPKv' has arcs to entry block
test_tile_elements.dir/test/tests/TileElements.cpp.gcno:'_ZN9__gnu_cxx13new_allocatorIcE8allocateEjPKv' has arcs from exit block
```
which we cannot alleviate, but they overload Travis' log size of 4MiB
causing the jobs to get killed.
This will simply silence those messages.
