Fix CMake 3.10 and below compatibility (#763)

Add empty list of sources to add_library and add_executable.

CMakeLists.txt

@@ -61,7 +61,7 @@ set(msvc-rt-mt-dll $<STREQUAL:${msvc-rt},MultiThreadedDLL>)
 
 set(backport-msvc-runtime $<VERSION_LESS:${CMAKE_VERSION},3.15>)
 
-add_library(yaml-cpp ${yaml-cpp-type})
+add_library(yaml-cpp ${yaml-cpp-type} "")
 add_library(yaml::yaml ALIAS yaml-cpp)
 
 set_property(TARGET yaml-cpp

test/CMakeLists.txt

@@ -20,7 +20,7 @@ endif()
 file(GLOB test-new-api-sources ${test-new-api-pattern})
 file(GLOB test-sources ${test-source-pattern})
 
-add_executable(yaml-cpp-tests)
+add_executable(yaml-cpp-tests "")
 target_sources(yaml-cpp-tests
   PRIVATE
     ${test-new-api-sources}