Fixes https://github.com/nomic-ai/gpt4all/issues/1760 LLModel ERROR: Could not find CPU LLaMA implementation.

Inspired by Microsoft docs for LoadLibraryExA (https://learn.microsoft.com/en-us/windows/win32/api/libloaderapi/nf-libloaderapi-loadlibraryexa).
When using LOAD_LIBRARY_SEARCH_DLL_LOAD_DIR, the lpFileName parameter must specify a fully qualified path, also it needs to be backslashes (\), not forward slashes (/).

gpt4all-backend/dlhandle.h

@@ -54,6 +54,7 @@ public:
 };
 #else
 #include <string>
+#include <algorithm>
 #include <exception>
 #include <stdexcept>
 #ifndef NOMINMAX
@@ -75,7 +76,9 @@ public:
 
     Dlhandle() : chandle(nullptr) {}
     Dlhandle(const std::string& fpath) {
-        chandle = LoadLibraryExA(fpath.c_str(), NULL, LOAD_LIBRARY_SEARCH_DEFAULT_DIRS | LOAD_LIBRARY_SEARCH_DLL_LOAD_DIR);
+        std::string path = fpath;
+        std::replace(path.begin(), path.end(), '/', '\\');
+        chandle = LoadLibraryExA(path.c_str(), NULL, LOAD_LIBRARY_SEARCH_DEFAULT_DIRS | LOAD_LIBRARY_SEARCH_DLL_LOAD_DIR);
         if (!chandle) {
             throw Exception("dlopen(\""+fpath+"\"): Error");
         }

gpt4all-backend/llmodel.cpp

@@ -104,7 +104,7 @@ const std::vector<LLModel::Implementation> &LLModel::Implementation::implementat
 
                     // Add to list if model implementation
                     try {
-                        Dlhandle dl(p.string());
+                        Dlhandle dl(std::filesystem::absolute(p).string());
                         if (!Implementation::isImplementation(dl)) {
                             continue;
                         }