Fix some dlx fails

Generic linker ELF targets using CREATE_OBJECT_SYMBOLS in their
scripts run into a problem.  The file symbols are created by
_bfd_generic_link_output_symbols in each object file, in the section
corresponding to the CREATE_OBJECT_SYMBOLS section, typically .text.
If it so happens that the output .text section is stripped due to
being empty, then elf.c:assign_section_numbers won't assign an ELF
section number and swap_out_syms will report "unable to find
equivalent output section" for the object symbols.  Fix this by
always keeping an output section with CREATE_OBJECT_SYMBOLS.

	* ldlang.c (lang_size_sections_1): Set SEC_KEEP on
	create_object_symbols_section.
	* testsuite/ld-elf/pr22319.d: Don't xfail dlx.

ld/ChangeLog

@@ -1,3 +1,9 @@
+2019-03-21  Alan Modra  <amodra@gmail.com>
+
+	* ldlang.c (lang_size_sections_1): Set SEC_KEEP on
+	create_object_symbols_section.
+	* testsuite/ld-elf/pr22319.d: Don't xfail dlx.
+
 2019-03-18  Alan Modra  <amodra@gmail.com>
 
 	* testsuite/ld-elf/merge.d: Remove csky from xfails, add moxie.

ld/ldlang.c

@@ -5619,8 +5619,9 @@ lang_size_sections_1
 	  break;
 
 	case lang_object_symbols_statement_enum:
-	  link_info.create_object_symbols_section =
-	    output_section_statement->bfd_section;
+	  link_info.create_object_symbols_section
+	    = output_section_statement->bfd_section;
+	  output_section_statement->bfd_section->flags |= SEC_KEEP;
 	  break;
 
 	case lang_output_statement_enum:

ld/testsuite/ld-elf/pr22319.d

@@ -1,8 +1,6 @@
 #name: PR 22319 - required undefined symbols in output
 #ld: -u undefined_symbol -e 0
 #nm: -u
-#xfail: dlx-*-* 
-# The DLX target fails because it needs a special linker script to handle file symbols.
 
 [ 	]+U+[ 	]+undefined_symbol
 #pass