[BUILD] Use fmt-header instead of libfmt (#1791)

test/CMakeLists.txt

@@ -97,7 +97,7 @@ if(BUILD_TESTS)
   target_link_libraries(rccl-UnitTests PRIVATE hip::host hip::device hsa-runtime64::hsa-runtime64)
   target_link_libraries(rccl-UnitTests PRIVATE Threads::Threads)
   target_link_libraries(rccl-UnitTests PRIVATE dl)
-  target_link_libraries(rccl-UnitTests PRIVATE fmt::fmt)
+  target_link_libraries(rccl-UnitTests PRIVATE fmt::fmt-header-only)
   if(OPENMP_TESTS_ENABLED)
     target_link_libraries(rccl-UnitTests PRIVATE "${OpenMP_CXX_FLAGS}")
   endif()