configure: add -Werror=int-conversion to extra compiler checks

This corresponds to new errors in gcc 14 according to #28441

configure.ac

@@ -1161,7 +1161,7 @@ AC_ARG_ENABLE([extra_checks],
                     [Turn some warnings into compilation error (default disabled)]),,
                     [enable_extra_checks="no"])
 AS_IF([test "${enable_extra_checks}" = "yes"], [
-    AX_APPEND_COMPILE_FLAGS([-Werror=missing-field-initializers -Werror=format -Werror=incompatible-pointer-types -Werror=restrict], [CFLAGS])
+    AX_APPEND_COMPILE_FLAGS([-Werror=missing-field-initializers -Werror=format -Werror=incompatible-pointer-types -Werror=restrict -Werror=int-conversion], [CFLAGS])
     AC_LANG_PUSH(C++)
     AX_APPEND_COMPILE_FLAGS([-Werror=missing-field-initializers -Werror=format], [CXXFLAGS])
     AC_LANG_POP(C++)