mips_gprel_reloc segfault

[Alan Modra <amodra@gmail.com>]

Not just the undefined section has a NULL owner, the absolute section
has too.  Which means we can't find output_bfd for __gp.  Also, may as
well test directly for output_bfd == NULL.

	* coff-mips.c (mips_gprel_reloc): Don't segfault on any of
	bfd_is_const_section sections.

diff --git a/bfd/coff-mips.c b/bfd/coff-mips.c
index 9614d338abe..d4dc1bd3c19 100644
--- a/bfd/coff-mips.c
+++ b/bfd/coff-mips.c
@@ -593,11 +593,10 @@ mips_gprel_reloc (bfd *abfd ATTRIBUTE_UNUSED,
     {
       relocatable = false;
       output_bfd = symbol->section->output_section->owner;
+      if (output_bfd == NULL)
+	return bfd_reloc_undefined;
     }
 
-  if (bfd_is_und_section (symbol->section) && ! relocatable)
-    return bfd_reloc_undefined;
-
   /* We have to figure out the gp value, so that we can adjust the
      symbol value correctly.  We look up the symbol _gp in the output
      BFD.  If we can't find it, we're stuck.  We cache it in the ECOFF

-- 
Alan Modra
Australia Development Lab, IBM