Update .travis.yml

[skip ci]
Update .travis.osx.yml

disable tcmalloc for OSX
Track memory usage. Add new CMake option TRACK_MEMORY_USAGE (It is ON by default).

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Update .travis.windows.yml

Explicitly turn off TCMALLOC for windows builds
[skip ci]
Update .travis.yml

- make TCMALLOC explicit
Add support for _msize

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Fix Check{MSize,MallocUsableSize}.cc and FindMSize.cmake to consider cross-compilation
Add support OSX's malloc_size