fix pkg-config generation for mingw

cmake/OpenCVUtils.cmake

@@ -1002,7 +1002,7 @@ endfunction()
 macro(ocv_get_libname var_name)
   get_filename_component(__libname "${ARGN}" NAME)
   # libopencv_core.so.3.3 -> opencv_core
-  string(REGEX REPLACE "^lib(.+)\\.(a|so)(\\.[.0-9]+)?$" "\\1" __libname "${__libname}")
+  string(REGEX REPLACE "^lib(.+)\\.(a|so|dll)(\\.[.0-9]+)?$" "\\1" __libname "${__libname}")
   # MacOSX: libopencv_core.3.3.1.dylib -> opencv_core
   string(REGEX REPLACE "^lib(.+[^.0-9])\\.([.0-9]+\\.)?dylib$" "\\1" __libname "${__libname}")
   set(${var_name} "${__libname}")