d: Fix ICE in in force_decl_die, at dwarf2out.c with -gdwarf-2 -gstrict-dwarf [PR98067]

Manifest constants in D are represented as CONST_DECLs, which can be
imported from one module to another.  However, when compiling on strict
dwarf2 targets such as *-*-darwin10, importing CONST_DECLs cannot be
represented in debug as D did not exist as an AT_language until dwarf3,
and the only available fallback being DW_LANG_C.  As CONST_DECLs are
treated as enumerators in C, and not outputted individually in
gen_decl_die, this causes an internal error in force_decl_die to occur.

To handle this, similar to other places in dwarf2out, if a CONST_DECL is
seen in dwarf2out_imported_module_or_decl_1, then we simply return early
if the language is not one of Ada, D, or Fortran.

gcc/ChangeLog:

	PR d/98067
	* dwarf2out.c (dwarf2out_imported_module_or_decl_1): Handle
	  CONST_DECL only if is_fortran, is_ada, or is_dlang.

gcc/testsuite/ChangeLog:

	PR d/98067
	* gdc.dg/debug/debug.exp: New test.
	* gdc.dg/debug/dwarf2/dwarf2.exp: New test.
	* gdc.dg/debug/dwarf2/imports/pr98067.d: New test.
	* gdc.dg/debug/dwarf2/langdw2.d: New test.
	* gdc.dg/debug/dwarf2/langdw3.d: New test.
	* gdc.dg/debug/dwarf2/pr98067.d: New test.
	* gdc.dg/debug/trivial.d: New test.

gcc/dwarf2out.c

@@ -26705,6 +26705,13 @@ dwarf2out_imported_module_or_decl_1 (tree decl,
 	      gen_type_die_for_member (type, decl,
 				       get_context_die (TYPE_CONTEXT (type)));
 	    }
+	  if (TREE_CODE (decl) == CONST_DECL)
+	    {
+	      /* Individual enumerators of an enum type do not get output here
+		 (see gen_decl_die), so we cannot call force_decl_die.  */
+	      if (!is_fortran () && !is_ada () && !is_dlang ())
+		return;
+	    }
 	  if (TREE_CODE (decl) == NAMELIST_DECL)
 	    at_import_die = gen_namelist_decl (DECL_NAME (decl),
 					 get_context_die (DECL_CONTEXT (decl)),

gcc/testsuite/gdc.dg/debug/debug.exp

@@ -0,0 +1,28 @@
+# Copyright (C) 2020 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+# 
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+# 
+# You should have received a copy of the GNU General Public License
+# along with GCC; see the file COPYING3.  If not see
+# <http://www.gnu.org/licenses/>.
+
+# Load support procs.
+load_lib gdc-dg.exp
+
+# Initialize `dg'.
+dg-init
+
+# Main loop.
+gcc-dg-debug-runtest gdc_target_compile trivial.d [list -O -O3] \
+    [lsort [glob -nocomplain $srcdir/$subdir/*.d]]
+
+# All done.
+dg-finish

gcc/testsuite/gdc.dg/debug/dwarf2/dwarf2.exp

@@ -0,0 +1,31 @@
+#   Copyright (C) 2020 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+# 
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+# 
+# You should have received a copy of the GNU General Public License
+# along with GCC; see the file COPYING3.  If not see
+# <http://www.gnu.org/licenses/>.
+
+# Load support procs.
+load_lib gdc-dg.exp
+
+# Main loop.
+set comp_output [gdc_target_compile \
+    "$srcdir/$subdir/../trivial.d" "trivial.S" assembly \
+    "additional_flags=-gdwarf"]
+if { ! [string match "*: target system does not support the * debug format*" \
+    $comp_output] } {
+    remove-build-file "trivial.S"
+    gdc-dg-runtest [lsort [glob -nocomplain $srcdir/$subdir/*.d ] ] "" "-gdwarf"
+}
+
+# All done.
+dg-finish

gcc/testsuite/gdc.dg/debug/dwarf2/imports/pr98067.d

@@ -0,0 +1,3 @@
+module imports.pr98067;
+
+enum MAP_ANON = 0x10;

gcc/testsuite/gdc.dg/debug/dwarf2/langdw2.d

@@ -0,0 +1,7 @@
+// DW_LANG_D is not available in dwarf2, so we should produce DW_LANG_C (0x2)
+// as AT_language.
+// { dg-do compile }
+// { dg-options "-gdwarf-2 -gstrict-dwarf -dA" }
+// { dg-final { scan-assembler "0x2\[^\n\r\]*AT_language" } }
+
+module langdw2;

gcc/testsuite/gdc.dg/debug/dwarf2/langdw3.d

@@ -0,0 +1,6 @@
+// We should produce DW_LANG_D (0x13) as AT_language.
+// { dg-do compile }
+// { dg-options "-gdwarf-3 -dA" }
+// { dg-final { scan-assembler "0x13\[^\n\r\]*AT_language" } }
+
+module langdw3;

gcc/testsuite/gdc.dg/debug/dwarf2/pr98067.d

@@ -0,0 +1,6 @@
+// https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98067
+// { dg-options "-gdwarf-2 -gstrict-dwarf -I $srcdir/gdc.dg/debug/dwarf2" }
+// { dg-do compile }
+module pr98067;
+
+import imports.pr98067 : MAP_ANON;

gcc/testsuite/gdc.dg/debug/trivial.d

@@ -0,0 +1,6 @@
+/* { dg-do run } */
+
+int main()
+{
+    return 0;
+}