gdb compilation failure on AIX.

Hi All,

GDB is failing to compile on AIX.
https://gdb-build.sergiodj.net/builders/AIX-POWER8-plain/builds/1905/steps/compile%20gdb/logs/stdio

This is because of fork-inferior.o isn't being include during the final 
step of creating gdb binary.
I guess this is mostly becuase of some of the recent change. I need to 
check the history yet.

This patch should resolve this final linking issue.

--- ./gdb/configure.nat_orig    2017-06-13 02:05:59.000000000 -0500
+++ ./gdb/configure.nat 2017-06-13 02:19:41.000000000 -0500
@@ -88,7 +88,7 @@
                # Host: IBM PowerPC running AIX aix-thread.o is not
                # listed in NATDEPFILES as it is pulled in by
                # configure.
-               NATDEPFILES='fork-child.o inf-ptrace.o rs6000-nat.o'
+               NATDEPFILES='fork-child.o inf-ptrace.o rs6000-nat.o 
fork-inferior.o'
 
                # When compiled with cc, for debugging, this argument
                # should be passed.  We have no idea who our current

Let me know if this is fine. 

Thanks,
-Sangamesh