Add more function stubs for libc++ 23 on Windows

These are needed by libc++ when targeting Windows since
https://github.com/llvm/llvm-project/commit/8a531c3608c722ad529be448d6ecef06ba107228,
which is included in libc++ 23.

In a very brief test, it seems like we don't need to actually
implement them.

Source/Windows/Common/WinAPI/Misc.cpp

@@ -188,3 +188,11 @@ DLLEXPORT_FUNC(LONG, RegCloseKey, (HKEY hKey)) {
 DLLEXPORT_FUNC(DWORD, GetActiveProcessorCount, (WORD group)) {
   UNIMPLEMENTED();
 }
+
+DLLEXPORT_FUNC(UINT, GetACP, ()) {
+  UNIMPLEMENTED();
+}
+
+DLLEXPORT_FUNC(int, GetLocaleInfoEx, (LPCWSTR lpLocaleName, LCTYPE LCType, LPWSTR lpLCData, int cchData)) {
+  UNIMPLEMENTED();
+}