Update bld_catkin_merge.bat.in

vinca/templates/bld_catkin_merge.bat.in

@@ -6,6 +6,13 @@ setlocal
 set CC=cl.exe
 set CXX=cl.exe
 
+:: ROS_BUILD_SHARED_LIBS is always defined in CMake by catkin
+:: if ROS (1) is build as shared library . However, some packages are not
+:: passing compilation flags from CMake to other build systems (such as qmake),
+:: so we enable it explicitly via the CL environment variable, see
+:: https://learn.microsoft.com/en-us/cpp/build/reference/cl-environment-variables?view=msvc-170
+set CL=/DROS_BUILD_SHARED_LIBS=1
+
 set CATKIN_MAKE_ISOLATED=src\ros-@(ros_distro)-catkin\bin\catkin_make_isolated
 set CMAKE_PREFIX_PATH=%CMAKE_PREFIX_PATH:\=/%