use LoadLibraryExA for absolute paths to libs only

- LoadLibraryExA with relative path and LOAD_LIBRARY_SEARCH_DLL_LOAD_DIR
  gives an incorrect parameter error
- LoadLibraryExA with relative path and LOAD_LIBRARY_SEARCH_DEFAULT_DIRS
  does not look into standard search paths like PATH
- thus use LoadLibraryA again when libname seems to be relative path
- fixes #759

ChangeLog.md

@@ -7,6 +7,11 @@ More detailed information about incremental changes can be found in the
 
 ## 3.14
 
+### 3.14.16 (2024-04-22)
+
+- Fixed load of linear solver libraries at runtime on Windows, which got
+  broken for relative paths (the default) in 3.14.15 [#759].
+
 ### 3.14.15 (2024-04-10)
 
 - Fixed include guard of IpGenAugSystemSolver.hpp [#756, by Christopher Wellons].

src/Common/IpLibraryLoader.cpp

@@ -50,7 +50,14 @@ void LibraryLoader::loadLibrary()
    }
 
 #ifdef HAVE_WINDOWS_H
-   libhandle = (void*)LoadLibraryExA(libname.c_str(), NULL, LOAD_LIBRARY_SEARCH_DEFAULT_DIRS | LOAD_LIBRARY_SEARCH_DLL_LOAD_DIR);
+   /* if absolute path, then use LoadLibraryExA with LOAD_LIBRARY_SEARCH_DLL_LOAD_DIR to find
+    * dependencies of library in same directory
+    * otherwise, use standard search paths (which includes PATH)
+    */
+   if( libname.length() > 2 && libname[1] == ':' )
+      libhandle = (void*)LoadLibraryExA(libname.c_str(), NULL, LOAD_LIBRARY_SEARCH_DLL_LOAD_DIR);
+   else
+      libhandle = (void*)LoadLibraryA(libname.c_str());
 
    if( libhandle == NULL )
    {