[UR] Add missing Threads library to common

Before oneapi-src#1216 adapters linked with
disjoint_pool library that linked with Threads library.

PR oneapi-src#1216 replace disjoint_pool with a version from UMF library that does not link
with Threads lib explicitly which leads to compilation error on xmain. Fix this
by explicitly adding adding Threads to ur_common.

Author: igchor

source/common/CMakeLists.txt

@@ -47,3 +47,10 @@ target_link_libraries(ur_common PUBLIC
     ${CMAKE_DL_LIBS}
     ${PROJECT_NAME}::headers
 )
+
+if (UNIX)
+    set(CMAKE_THREAD_PREFER_PTHREAD TRUE)
+    set(THREADS_PREFER_PTHREAD_FLAG TRUE)
+    find_package(Threads REQUIRED)
+    target_link_libraries(ur_common PUBLIC Threads::Threads)
+endif()