Link Threads::Threads (#119)

`pthread.h` is included in `src/common.h` but lib is not properly
linked, resulting in the build failing with unresolved symbols when
trying to link.

[ROCm/rccl-tests commit: 5b27b961b2]

projects/rccl-tests/src/CMakeLists.txt

@@ -126,7 +126,7 @@ add_custom_target(git_version_check
 add_custom_target(hipify DEPENDS ${HIP_COMMON_SOURCES})
 add_library(rccl_common OBJECT ${HIP_COMMON_SOURCES})
 add_dependencies(rccl_common hipify git_version_check)
-target_link_libraries(rccl_common roc::rccl hip::device)
+target_link_libraries(rccl_common roc::rccl hip::device Threads::Threads)
 if(USE_MPI)
   target_link_libraries(rccl_common MPI::MPI_CXX)
 endif()