gcc: avoid generating negative values to DW_AT_byte_size.

There is a bug in gcc (GCC/35998) where dwarf reports
sizes of unsigned -1 (0xffffffff).

On NetBSD this generated a faulty CTF entry which then
caused a segfault in ctfmerge. The issue was worked
around in NetBSD's Dtrace but since the issue originated
in gcc, it seems reasonable to fix it here.

Upstream gcc has been slow to react to this issue and
the author that submitted the patch is not interested
in licensing the change to us, so I did an independent
workaround for the issue.

MFC after:	1 week

1 files changed, 3 insertions, 3 deletions

diff --git a/contrib/gcc/dwarf2out.c b/contrib/gcc/dwarf2out.c
index 25a906b..453e653 100644
--- a/contrib/gcc/dwarf2out.c
+++ b/contrib/gcc/dwarf2out.c
@@ -10812,9 +10812,9 @@ add_byte_size_attribute (dw_die_ref die, tree tree_node)
 
   /* Note that `size' might be -1 when we get to this point.  If it is, that
      indicates that the byte size of the entity in question is variable.  We
-     have no good way of expressing this fact in Dwarf at the present time,
-     so just let the -1 pass on through.  */
-  add_AT_unsigned (die, DW_AT_byte_size, size);
+     have no good way of expressing this fact in Dwarf at the present time.
+     GCC/35998: Avoid passing negative sizes to Dtrace and gdb.  */
+  add_AT_unsigned (die, DW_AT_byte_size, (size > 0 ? size : 0));
 }
 
 /* For a FIELD_DECL node which represents a bit-field, output an attribute