[libc] Fix atexit not getting linked on linux (llvm#98537)

Atexit needs to be linked into exit on linux since atexit defines
__cxa_finalize. This should probably be fixed a different way but this
works for now.

Author: michaelrj-google

libc/src/stdlib/CMakeLists.txt

@@ -497,15 +497,24 @@ add_entrypoint_object(
     .exit_handler
 )
 
+list(APPEND exit_deps
+  libc.src.__support.OSUtil.osutil
+  ._Exit
+)
+if (NOT LIBC_TARGET_OS_IS_BAREMETAL)
+  list(APPEND exit_deps
+    .atexit
+  )
+endif()
+
 add_entrypoint_object(
   exit
   SRCS
     exit.cpp
   HDRS
     exit.h
   DEPENDS
-    ._Exit
-    libc.src.__support.OSUtil.osutil
+    ${exit_deps}
 )
 
 add_entrypoint_object(