Fix gdb.multi/base.exp testsuite regression

Fix gdb.multi/base.exp testsuite regression

Regressed by:

commit 762f774785f4ef878ac4c831e1f4733dc957234d
Author: Pedro Alves <palves@redhat.com>
Date:   Thu Dec 10 16:21:06 2015 +0000
    Stop using nowarnings in gdb/testsuite/gdb.multi/

+gdb compile failed, gdb/testsuite/gdb.multi/hello.c: In function 'commonfun':
+gdb/testsuite/gdb.multi/hello.c:24:19: warning: implicit declaration of function 'bar' [-Wimplicit-function-declaration]
+ int commonfun() { bar(); } /* from hello */
+                   ^
+gdb/testsuite/gdb.multi/hello.c: At top level:
+gdb/testsuite/gdb.multi/hello.c:26:1: warning: return type defaults to 'int' [-Wimplicit-int]
+ bar()
+ ^
+gdb/testsuite/gdb.multi/hello.c:32:1: warning: return type defaults to 'int' [-Wimplicit-int]
+ hello(int x)
+ ^
+gdb/testsuite/gdb.multi/hello.c:38:1: warning: return type defaults to 'int' [-Wimplicit-int]
+ main()
+ ^
+UNTESTED: gdb.multi/base.exp: base.exp

gdb/testsuite/ChangeLog
2016-01-08  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* gdb.multi/goodbye.c: Fix compilation warnings by adding return types
	and reordering the functions.
	* gdb.multi/hangout.c: Likewise.
	* gdb.multi/hello.c: Likewise.