fix: define c++14 standard in CMakeLists.txt

CMakeLists.txt

@@ -46,9 +46,16 @@ add_library(sylvan
     tls.h
 )
 
+set_target_properties(sylvan PROPERTIES
+  CXX_STANDARD 14
+  CXX_STANDARD_REQUIRED YES
+  CXX_EXTENSIONS NO
+)
+
 target_link_libraries(sylvan -lpthread)
 target_link_libraries(sylvan -lgmp)
 
 if(UNIX AND NOT APPLE)
     target_link_libraries(sylvan rt)
 endif()
+