Silence ABI warnings with GCC 14

With the previous flag, GCC 14 displays many warnings like "warning: the mangled name of ... changed between ‘-fabi-version=17’ and ‘-fabi-version=19’ [-Wabi]"
I think these warnings are not useful for us. Since PCL 1.15.0 will not be ABI-compatible to PCL 1.14.1 anyway, these name changes do not matter AFAIK.

CMakeLists.txt

@@ -117,7 +117,7 @@ endif()
 if(CMAKE_COMPILER_IS_GNUCXX)
   if("${CMAKE_CXX_FLAGS}" STREQUAL "${CMAKE_CXX_FLAGS_DEFAULT}")
     if (CMAKE_CXX_COMPILER_VERSION VERSION_GREATER 7)
-      string(APPEND CMAKE_CXX_FLAGS " -Wabi=11")
+      string(APPEND CMAKE_CXX_FLAGS " -Wabi=18")
     else()
       string(APPEND CMAKE_CXX_FLAGS " -Wabi")
     endif()