Allow calling of variadic C++ functions

Currently, it's not possible to call a variadic C++ function:
```
(gdb) print sum_vararg_int(1, 10)
Cannot resolve function sum_vararg_int to any overloaded instance
(gdb) print sum_vararg_int(2, 20, 30)
Cannot resolve function sum_vararg_int to any overloaded instance
```

It's because all additional arguments get the TOO_FEW_PARAMS_BADNESS
rank by rank_function, which disqualifies the function.

To fix this, I've created the new VARARG_BADNESS rank, which is
used only for additional arguments of variadic functions, allowing
them to be called:
```
(gdb) print sum_vararg_int(1, 10)
$1 = 10
(gdb) print sum_vararg_int(2, 20, 30)
$2 = 50
```

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=28589
Approved-By: Tom Tromey <tom@tromey.com>

2 files changed, 39 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.cp/call-c.cc b/gdb/testsuite/gdb.cp/call-c.cc
index 4362bbf..1677755 100644
--- a/gdb/testsuite/gdb.cp/call-c.cc
+++ b/gdb/testsuite/gdb.cp/call-c.cc
@@ -15,6 +15,8 @@
    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
 
+#include <stdarg.h>
+
 int func(int x)
 {
    return x;
@@ -33,6 +35,29 @@ extern "C" {
   int foo(int);
 }
 
+int sum_vararg_int (int count, ...)
+{
+  va_list va;
+  int sum = 0;
+
+  va_start (va, count);
+  for (int i = 0; i < count; i++)
+    sum += va_arg (va, int);
+  va_end (va);
+
+  return sum;
+}
+
+int vararg_func (int a, ...)
+{
+  return 1;
+}
+
+int vararg_func (int a, int b, ...)
+{
+  return 2;
+}
+
 int main()
 {
     Foo f;
@@ -41,5 +66,6 @@ int main()
     FooHandle handle = pf;
     rf->func(); /* set breakpoint here */
     foo(0);
+    sum_vararg_int (1, 5);
     return func(0);
 }
diff --git a/gdb/testsuite/gdb.cp/call-c.exp b/gdb/testsuite/gdb.cp/call-c.exp
index b20bc86..36c0c1e 100644
--- a/gdb/testsuite/gdb.cp/call-c.exp
+++ b/gdb/testsuite/gdb.cp/call-c.exp
@@ -38,5 +38,18 @@ gdb_test "print foo(1)" "\\\$$decimal = 1"
 gdb_test "continue" ".*breakpoint here.*" "continue to bp"
 gdb_test "print rf->func()" "\\\$$decimal = 1"
 
+gdb_test "print sum_vararg_int(0)" "0"
+gdb_test "print sum_vararg_int(1, 10)" "10"
+gdb_test "print sum_vararg_int(2, 20, 30)" "50"
+gdb_test "print sum_vararg_int(5, 20, 30, 40, 50, 60)" "200"
+
+gdb_test "print vararg_func(1)" "1"
+gdb_test "print vararg_func(2, 3)" "2"
+gdb_test "print vararg_func(4, 5.5)" "2"
+gdb_test "print vararg_func(6, \"7\")" "1"
+gdb_test "print vararg_func(8, 9, 10)" "2"
+gdb_test "print vararg_func(11, 12, 13.5)" "2"
+gdb_test "print vararg_func(14, 15, \"16\")" "2"
+
 # Regression test for method call via a typedef.
 gdb_test "print handle->func()" "\\\$$decimal = 1"