[libc] Fix wrapper headers for at_quick_exit on GLIBC

Summary:
GLIBC likes to define this with the C++ linkage in the header, which
conflict. For now just hack around it by pretending it's `atexit` since
it has the same signature.

Author: jhuber6

clang/lib/Headers/llvm_libc_wrappers/stdlib.h

@@ -34,8 +34,16 @@ _Static_assert(__builtin_offsetof(div_t, quot) == 0, "ABI mismatch!");
 _Static_assert(__builtin_offsetof(ldiv_t, quot) == 0, "ABI mismatch!");
 _Static_assert(__builtin_offsetof(lldiv_t, quot) == 0, "ABI mismatch!");
 
+#if defined(__GLIBC__) && __cplusplus >= 201703L
+#define at_quick_exit atexit
+#endif
+
 #include <llvm-libc-decls/stdlib.h>
 
+#if defined(__GLIBC__) && __cplusplus >= 201703L
+#undef at_quick_exit
+#endif
+
 #pragma omp end declare target
 
 #undef __LIBC_ATTRS