Add LibUnwind as a dependency of glog::glog (#101)

[Atry]

Summary: X-link: https://github.com/facebookincubator/hsthrift/pull/101

X-link: https://github.com/facebookincubator/katran/pull/172

X-link: https://github.com/facebookincubator/mvfst/pull/273

X-link: https://github.com/fairinternal/AIRStore/pull/38

LibUnwind is a dependency of glog according to objdump. This diff adds ${LIBUNWIND_LIBRARY} to the CMake imported library glog::glog as an element in the IMPORTED_LINK_INTERFACE_LIBRARIES property.

Without this diff, there will be a linker error like this:

/usr/bin/ld: /usr/lib/x86_64-linux-gnu/libglog.so: undefined reference to symbol '_Ux86_64_getcontext'
//usr/lib/x86_64-linux-gnu/libunwind.so.8: error adding symbols: DSO missing from command line
collect2: error: ld returned 1 exit status

Differential Revision: D39340650

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D39340650

[yancouto]

A lot has changed in the OSS build with the recent Sapling release, so I'm closing this. If you still can't build and this helps, please reopen.