Allow opening file on multiple units

As of Fortran 2018 it's allowed to open the same file on multiple
units.

libgfortran/ChangeLog:

2019-05-15  Janne Blomqvist  <jb@gcc.gnu.org>

	PR fortran/90461
        * io/open.c (new_unit): Don't check if the file is already open
	for F2018.

testsuite/ChangeLog:

2019-05-15  Janne Blomqvist  <jb@gcc.gnu.org>

	PR fortran/90461
        * gfortran.dg/open_errors_2.f90: Add -std=f2008, adjust line number.
	* gfortran.dg/open_errors_3.f90: New test.

From-SVN: r271260

gcc/testsuite/ChangeLog

+2019-05-15  Janne Blomqvist  <jb@gcc.gnu.org>
+
+	PR fortran/90461
+        * gfortran.dg/open_errors_2.f90: Add -std=f2008, adjust line number.
+	* gfortran.dg/open_errors_3.f90: New test.
+
 2019-05-15  H.J. Lu  <hongjiu.lu@intel.com>
 
 	PR target/89021

gcc/testsuite/gfortran.dg/open_errors_2.f90

 ! { dg-do run }
+! { dg-options "-std=f2008" }
 ! { dg-shouldfail "runtime error" }
-! { dg-output "At line 13.*File already opened" }
+! { dg-output "At line 14.*File already opened" }
 
 ! PR 65563 - this used to segfault for some versions.
   variable_1 = 0

gcc/testsuite/gfortran.dg/open_errors_3.f90

+! { dg-do  run }
+! PR 90461 Open file on multiple units as of F2018
+program openmult
+  implicit none
+  character(len=*), parameter :: fname="pr90461.dat"
+  open(10, file=fname, form="unformatted")
+  open(11, file=fname, form="unformatted")
+  close(11)
+  close(10, status="delete")
+end program openmult
+! { dg-final { remote_file build delete "pr90461.dat" } }

libgfortran/ChangeLog

+2019-05-15  Janne Blomqvist  <jb@gcc.gnu.org>
+
+	PR fortran/90461
+        * io/open.c (new_unit): Don't check if the file is already open
+	for F2018.
+
 2019-05-02  Jakub Jelinek  <jakub@redhat.com>
 
 	* Makefile.am (gfor_cdir): Remove $(MULTISUBDIR).

libgfortran/io/open.c

@@ -515,7 +515,8 @@ new_unit (st_parameter_open *opp, gfc_unit *u, unit_flags *flags)
      Do not error if opening file preconnected to stdin, stdout, stderr.  */
 
   u2 = NULL;
-  if ((opp->common.flags & IOPARM_OPEN_HAS_FILE) != 0)
+  if ((opp->common.flags & IOPARM_OPEN_HAS_FILE) != 0
+      && !(compile_options.allow_std & GFC_STD_F2018))
     u2 = find_file (opp->file, opp->file_len);
   if (u2 != NULL
       && (options.stdin_unit < 0 || u2->unit_number != options.stdin_unit)