if libatomic is found only link it if libgcc is the rtlib
Index: llvm-toolchain-snapshot_18~++20231213094656+c02d07fdf007/libcxx/CMakeLists.txt
===================================================================
--- llvm-toolchain-snapshot_18~++20231213094656+c02d07fdf007.orig/libcxx/CMakeLists.txt
+++ llvm-toolchain-snapshot_18~++20231213094656+c02d07fdf007/libcxx/CMakeLists.txt
@@ -685,13 +685,16 @@ function(cxx_link_system_libraries targe
       endif()
     elseif (LIBCXX_HAS_GCC_LIB)
       target_link_libraries(${target} PRIVATE gcc)
+      if (LIBCXX_HAS_ATOMIC_LIB)
+        target_link_libraries(${target} PRIVATE atomic)
+      endif()
     elseif (LIBCXX_HAS_GCC_S_LIB)
       target_link_libraries(${target} PRIVATE gcc_s)
     endif()
-  endif()
 
-  if (LIBCXX_HAS_ATOMIC_LIB)
-    target_link_libraries(${target} PRIVATE atomic)
+    if (LIBCXX_HAS_ATOMIC_LIB)
+      target_link_libraries(${target} PRIVATE atomic)
+    endif()
   endif()
 
   if (MINGW)