Use INTERFACE to pass on unicode dependency

Linking the cxxopts library with the unicode libraries and specifying
INTERFACE should ensure executables that link with cxxopts will also
link with the unicode libraries.

CMakeLists.txt

@@ -57,6 +57,11 @@ target_include_directories(
   cxxopts INTERFACE
   include/
   )
+target_link_libraries(
+  cxxopts
+  INTERFACE ${CXXOPTS_LINKER_LIBRARIES}
+  )
+
 
 add_subdirectory(src)
 add_subdirectory(test)

src/CMakeLists.txt

@@ -20,7 +20,7 @@
 
 if(CXXOPTS_BUILD_EXAMPLES)
     add_executable(example example.cpp)
-    target_link_libraries(example cxxopts ${CXXOPTS_LINKER_LIBRARIES})
+    target_link_libraries(example cxxopts)
 
     if (MSVC)
         target_compile_options(example PUBLIC /W2)

test/CMakeLists.txt

@@ -1,6 +1,6 @@
 if (CXXOPTS_BUILD_TESTS)
     add_executable(options_test options.cpp)
-    target_link_libraries(options_test cxxopts ${CXXOPTS_LINKER_LIBRARIES})
+    target_link_libraries(options_test cxxopts)
 
     if (MSVC)
         target_compile_options(options_test PUBLIC /W2)