backend: fix #includes with include-what-you-use (#2371)

Also fix a PARENT_SCOPE warning when building the backend.

Signed-off-by: Jared Van Bortel <jared@nomic.ai>

gpt4all-backend/llmodel.cpp

@@ -1,10 +1,13 @@
 #include "llmodel.h"
 
+#include "dlhandle.h"
+
 #include <cassert>
 #include <cstdlib>
 #include <filesystem>
 #include <fstream>
 #include <iostream>
+#include <iterator>
 #include <memory>
 #include <optional>
 #include <regex>
@@ -13,9 +16,6 @@
 #include <unordered_map>
 #include <vector>
 
-#include "dlhandle.h"
-#include "sysinfo.h"
-
 #ifdef _WIN32
 #   define WIN32_LEAN_AND_MEAN
 #   ifndef NOMINMAX
@@ -28,6 +28,10 @@
 #   include <intrin.h>
 #endif
 
+#if defined(__APPLE__) && defined(__aarch64__)
+#   include "sysinfo.h" // for getSystemTotalRAMInBytes
+#endif
+
 namespace fs = std::filesystem;
 
 #ifndef __APPLE__