[libc] Match stdlib.h baremetal entrypoints with types (#85030)

To match the entrypoints and types for baremetal, we need to include
__qsortrcompare_t and omit __atexithandler_t.

Author: petrhosek

libc/config/baremetal/api.td

@@ -64,7 +64,7 @@ def StdlibAPI : PublicAPI<"stdlib.h"> {
     "size_t",
     "__bsearchcompare_t",
     "__qsortcompare_t",
-    "__atexithandler_t",
+    "__qsortrcompare_t",
   ];
 }