Try

 -l "C:\Program Files\Common Files\Pr
+oduct\4.1\dptcpiphi.dll" ';
[download]

because https://gcc.gnu.org/onlinedocs/gcc/Invoking-GCC.html-L is for library paths to find -l libraryname in

Its easier to manage http://gcc.gnu.org/onlinedocs/gcc/Environment-Variables.html like C_INCLUDE_PATH/LIBRARY_PATH...