Fix build on *BSD (#10)

CMakeLists.txt

@@ -56,6 +56,13 @@ if(WIN32)
         libutp_inet_ntop.h)
 endif()
 
+if(CMAKE_VERSION VERSION_LESS 3.25)
+    set(BSD OFF)
+    if(CMAKE_SYSTEM_NAME MATCHES "BSD")
+        set(BSD ON)
+    endif()
+endif()
+
 add_library(libutp ${LIBUTP_LIBRARY_TYPE}
     include/libutp/utp.h
     include/libutp/utp_types.h
@@ -118,7 +125,7 @@ if(LIBUTP_BUILD_PROGRAMS AND NOT MSVC)
 
     target_compile_definitions(ucat
         PRIVATE
-            $<$<NOT:$<BOOL:${WIN32}>>:_POSIX_C_SOURCE=200112L>
+            $<$<NOT:$<OR:$<BOOL:${WIN32}>,$<BOOL:${BSD}>>>:_POSIX_C_SOURCE=200112L>
             $<$<BOOL:${APPLE}>:_DARWIN_C_SOURCE>)
 
     target_link_libraries(ucat