Checks all calls resolve to functions within correct namespace.

// Implementation inside the LIBC_NAMESPACE namespace.
// Correct if:
// - LIBC_NAMESPACE is a macro
// - LIBC_NAMESPACE expansion starts with `__llvm_libc`
namespace LIBC_NAMESPACE {

// Allow calls with the fully qualified name.

// Allow calls to compiler provided functions.

// Bare calls are allowed as long as they resolve to the correct namespace.

// Disallow calling into functions in the global namespace.

} // namespace LIBC_NAMESPACE