[gdb/testsuite] Fix wrong return type in tests

The following tests are marked untested with latest GCC due to a warning
being emitted for a mismatch between their return type and what the lack
of return statement:

* gdb.cp/breakpoint.exp
* gdb.cp/psymtab-parameter.exp
* gdb.cp/shadow.exp

This patch fix the return type to match the function definitions.

2017-11-29  Thomas Preud'homme  <thomas.preudhomme@arm.com>

gdb/testsuite/
	* gdb.cp/breakpoint.cc (bar): Set return type to void.
	* gdb.cp/psymtab-parameter.cc (func): Likewise.
	* gdb.cp/psymtab-parameter.exp: Update comment regarding prototype of
	func ().
	* gdb.cp/shadow.cc (B.func): Return 0.

gdb/testsuite/ChangeLog

@@ -1,3 +1,11 @@
+2017-11-29  Thomas Preud'homme  <thomas.preudhomme@arm.com>
+
+	* gdb.cp/breakpoint.cc (bar): Set return type to void.
+	* gdb.cp/psymtab-parameter.cc (func): Likewise.
+	* gdb.cp/psymtab-parameter.exp: Update comment regarding prototype of
+	func ().
+	* gdb.cp/shadow.cc (B.func): Return 0.
+
 2017-11-27  Joel Brobecker  <brobecker@adacore.com>
 
 	* gdb.ada/mi_catch_ex.exp (continue_to_exception): Adjust

gdb/testsuite/gdb.cp/breakpoint.cc

@@ -28,7 +28,7 @@ public:
     return 1; // conditional breakpoint in method
   }
 
-  int bar ()
+  void bar ()
   {
     for (int i = 0; i < 1; ++i)
       {

gdb/testsuite/gdb.cp/psymtab-parameter.cc

@@ -16,7 +16,7 @@
    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
 
 template <typename T>
-long
+void
 func ()
 {
 }

gdb/testsuite/gdb.cp/psymtab-parameter.exp

@@ -31,6 +31,6 @@ gdb_test_no_output "set language c++"
 # XFAIL than FAIL here.  For example -readnow breaks it.
 gdb_test_no_output "maintenance info symtabs"
 
-# GDB has shown only the `long func<short>()' ELF symbol before, not the DWARF
+# GDB has shown only the `void func<short>()' ELF symbol before, not the DWARF
 # symbol
 gdb_test "complete p 'func<short>(" "p 'func<short>\\(\\)"

gdb/testsuite/gdb.cp/shadow.cc

@@ -36,6 +36,7 @@ public:
               }
           }
       }
+    return 0;
   }
 };