Commit r269139 fixed an accidental dependency on MPFR 3.0. As we now
require at least MPFR 3.1.0+ we can revert it and instead use the
simpler MPFR 3.0+ code.

ChangeLog entry of the original commit was:

2019-02-23  David Malcolm  <dmalcolm@redhat.com>
            Jakub Jelinek  <jakub@redhat.com>

        PR middle-end/88074
        * simplify.c (norm2_do_sqrt, gfc_simplify_norm2): Use
        mpfr_number_p && !mpfr_zero_p instead of mpfr_regular_p.
        (norm2_add_squared): Likewise.  Use mp_exp_t rather than mpfr_exp_t.

ChangeLog for this commit:

2019-11-20  Janne Blomqvist  <jb@gcc.gnu.org>

	PR fortran/92463
	Revert r269139
	* simplify.c (norm2_do_sqrt, gfc_simplify_norm2): Use
	mpfr_regular_p instead of mpfr_number_p && !mpfr_zero_p.
	(norm2_add_squared): Likewise.  Use mpfr_exp_t rather than
	mp_exp_t.

From-SVN: r278525