(lldb) Fix PATH_MAX for Windows (#104493)

The build break was caused by a [previous
patch](#102223) using
`PATH_MAX` which is undefined in Windows.

Author: royitaqi

lldb/source/Utility/RealpathPrefixes.cpp

@@ -8,6 +8,7 @@
 
 #include "lldb/Utility/RealpathPrefixes.h"
 
+#include "lldb/Host/PosixApi.h"
 #include "lldb/Utility/FileSpec.h"
 #include "lldb/Utility/FileSpecList.h"
 #include "lldb/Utility/LLDBLog.h"