[libc] Match baremetal stdlib.h entrypoints with types

To match the entrypoints and types we need to exclude __atexithandler_t
and __qsortrcompare_t, as well as qsort_r, which is a GNU extension.

This is a reland of llvm/llvm-project#85030.

GitOrigin-RevId: 6666b3fca848c2562ad2e7470827561894246a6e
3 files changed