[FYI] Fix gdb mingw build

[Tom Tromey <tom@tromey.com>]

I noticed that the mingw build was failing in the buildbot.  This
patch fixes the problem.  I'm checking it in as obvious.

gdb/ChangeLog
2018-06-08  Tom Tromey  <tom@tromey.com>

	* windows-nat.c (windows_nat_target::xfer_partial): "beneath" is
	now a method.
---
 gdb/ChangeLog     |  5 +++++
 gdb/windows-nat.c | 12 ++++++------
 2 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 4f732b5b81..a10155bd95 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,8 @@
+2018-06-08  Tom Tromey  <tom@tromey.com>
+
+	* windows-nat.c (windows_nat_target::xfer_partial): "beneath" is
+	now a method.
+
 2018-06-08  Tom Tromey  <tom@tromey.com>
 
 	* btrace.c (parse_xml_raw): Use gdb::unique_xmalloc_ptr.
diff --git a/gdb/windows-nat.c b/gdb/windows-nat.c
index e3e36cdc3e..63a780014a 100644
--- a/gdb/windows-nat.c
+++ b/gdb/windows-nat.c
@@ -2953,8 +2953,8 @@ windows_xfer_shared_libraries (struct target_ops *ops,
 enum target_xfer_status
 windows_nat_target::xfer_partial (enum target_object object,
 				  const char *annex, gdb_byte *readbuf,
-				  const gdb_byte *writebuf, ULONGEST offset, ULONGEST len,
-				  ULONGEST *xfered_len)
+				  const gdb_byte *writebuf, ULONGEST offset,
+				  ULONGEST len, ULONGEST *xfered_len)
 {
   switch (object)
     {
@@ -2966,16 +2966,16 @@ windows_nat_target::xfer_partial (enum target_object object,
 					    writebuf, offset, len, xfered_len);
 
     default:
-      if (beneath == NULL)
+      if (beneath () == NULL)
 	{
 	  /* This can happen when requesting the transfer of unsupported
 	     objects before a program has been started (and therefore
 	     with the current_target having no target beneath).  */
 	  return TARGET_XFER_E_IO;
 	}
-      return beneath->xfer_partial (object, annex,
-				    readbuf, writebuf, offset, len,
-				    xfered_len);
+      return beneath ()->xfer_partial (object, annex,
+				       readbuf, writebuf, offset, len,
+				       xfered_len);
     }
 }
 
-- 
2.14.4