Update .travis.osx.yml

- make TCMALLOC explicit
[skip ci]
Add simple formatter tests

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Add max_sharing tests

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Add tests for memory.cpp

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Suppress cmake warning for OSX build
Undo the previous change which caused compile-errors
Update Find{MSize,MallocSize,MallocUsableSize}.cmake to handle the case where find_path fails