cannot build the object library (COOLPROP_OBJECT_LIBRARY)

[dongkeun-oh]

Description

The option of COOLPROP_OBJECT_LIBRARY doesn't work; this option is necessary to build libExternalMedia.a or its DLL.

Steps to Reproduce

1. mkdir build; cd build
2. cmake .. -D COOLPROP_OBJECT_LIBRARY=ON

Expected behavior: making object files as supposed.

Actual behavior: error in configuration as below.
` cmake .. -DCOOLPROP_OBJECT_LIBRARY=ON
-- COOLPROP_INSTALL_PREFIX=/home/spinhalf/Work/ExternalMedia/externals/CoolProp.git/install_root
-- The C compiler identification is GNU 7.5.0
-- The CXX compiler identification is GNU 7.5.0
-- Check for working C compiler: /usr/bin/cc
-- Check for working C compiler: /usr/bin/cc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Detecting C compile features
-- Detecting C compile features - done
-- Check for working CXX compiler: /usr/bin/c++
-- Check for working CXX compiler: /usr/bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- CoolProp version: 6.4.2dev
-- Found PythonInterp: /usr/bin/python2.7 (found suitable version "2.7.17", minimum required is "2.7")
-- Found LibDL: /usr/lib/x86_64-linux-gnu/libdl.so
-- Looking for C++ include memory
-- Looking for C++ include memory - found
-- Performing Test HAVE_SHARED_PTR_IN_STD_NAMESPACE
-- Performing Test HAVE_SHARED_PTR_IN_STD_NAMESPACE - Success
-- Found shared_ptr in std namespace using header.
CMake Error at CMakeLists.txt:528 (target_link_libraries):
Object library target "CoolProp" may not link to anything.

-- Configuring incomplete, errors occurred!
See also "/home/spinhalf/Work/ExternalMedia/externals/CoolProp.git/build/CMakeFiles/CMakeOutput.log".
`

Versions

CoolProp Version: 6.4.2
Operating System and Version: Ubuntu 18.04.5 with gcc 7.5.0 (x86_64-linux-gnu)
Access Method: ExternalMedia library in OpenModelica

Additional Information

A recommend patch of CMakeLists.txt is attached here.
CMakeLists.patch.txt

[ibell]

Pull request please