PR 93592 - Invalid UP/DOWN rounding with EN descriptor.

PR 93592 - Invalid UP/DOWN rounding with EN descriptor.

The fix is obvious (I have added a comment). The tests are probably
an overkill, but it does not hurt.

libgfortran/ChangeLog:

	PR fortran/93592
	* io/write_float.def (build_float_string): Do not reset
	  nbefore for FMT_F and FMT_EN.

gcc/testsuite/ChangeLog:

	PR fortran/93592
	* gfortran.dg/fmt_en.f90: Adjust test.
	* gfortran.dg/fmt_en_rd.f90: New test.
	* gfortran.dg/fmt_en_rn.f90: New test.
	* gfortran.dg/fmt_en_ru.f90: New test.
	* gfortran.dg/fmt_en_rz.f90: New test.

(cherry picked from commit 05e0971bcf94a481cbfa2731484f024a67dbd4a5)