I just tried that 6623. The bug isn't fixed.
This is what i get from compiling a project:
mingw32-g++.exe -Wall  -g     -c "C:\[Sergio]\C++\C++ Projects\test\main.cpp" -o obj\Debug\main.o
mingw32-g++.exe  -o bin\Debug\test.exe obj\Debug\main.o   -enable-auto-import  -lcomctl32 -lgdi32 
  And from compiling a single file:
 mingw32-g++.exe   -c "C:\[Sergio]\C++\cGui Library\Examples\Button_Example.cpp" -o "C:\[Sergio]\C++\cGui Library\Examples\Button_Example.o"
 mingw32-g++.exe  -o "C:\[Sergio]\C++\cGui Library\Examples\Button_Example.exe" "C:\[Sergio]\C++\cGui Library\Examples\Button_Example.o" 
The difference is that when i build a project, it linkes the libraries i have setted  in Compiler & Debugger -> Linker Settings. So it works fine.
But when i build a single file, with NO project, it doesnt link the libraries, and it SHOULD. The building log, for this case should be:
 mingw32-g++.exe   -c "C:\[Sergio]\C++\cGui Library\Examples\Button_Example.cpp" -o "C:\[Sergio]\C++\cGui Library\Examples\Button_Example.o"
 mingw32-g++.exe  -o "C:\[Sergio]\C++\cGui Library\Examples\Button_Example.exe" "C:\[Sergio]\C++\cGui Library\Examples\Button_Example.o"
 -enable-auto-import  -lcomctl32 -lgdi32 
That seems easy to fix...