Link Threads::Threads (ROCm#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.

Author: marbre

CMakeLists.txt

@@ -124,9 +124,6 @@ endif()
 set(THREADS_PREFER_PTHREAD_FLAG ON)
 find_package(Threads REQUIRED)
 
-##Adding pthread flag for linking
-#set( CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -pthread")
-
 ## Check for HIP
 find_package(hip REQUIRED)
 message(STATUS "HIP compiler:     ${HIP_COMPILER}")

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()