* invoke.texi: Document -fdelete-null-pointer-checks

    * invoke.texi: Document -fdelete-null-pointer-checks
        * toplev.c (flag_delete_null_pointer_checks): New.
        (f_options): Add entry for -fdelete-null-pointer-checks.
        (rest_of_compilation): Conditionalize null pointer check
        elimination on flag_delete_null_pointer_checks.
        (main): If -O2 or greater, enable -fdelete-null-pointer-checks

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@29631 138bc75d-0d04-0410-961f-82ee72b054a4