c++: avoid testcase warning on arm

[Nathan Sidwell]

I've pushed this patch to avoid a warning introduced by 94426's change 
to linkage of lambda.

The arm eabi wants to emit the vtable, other abis don't.
nathan
--
Nathan Sidwell
diff --git i/gcc/testsuite/ChangeLog w/gcc/testsuite/ChangeLog
index dd2cb04916f..b98c72cdd2a 100644
--- i/gcc/testsuite/ChangeLog
+++ w/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2020-04-17  Nathan Sidwell  <nat...@acm.org>
+
+	PR c++/94608
+	* g++.dg/lto/pr83720_0.C: Add fn def to avoid warning on arm ABI.
+
 2020-04-17  Jakub Jelinek  <ja...@redhat.com>
 
 	PR rtl-optimization/94618
diff --git i/gcc/testsuite/g++.dg/lto/pr83720_0.C w/gcc/testsuite/g++.dg/lto/pr83720_0.C
index 4e63c9be7cd..91f36caf2c0 100644
--- i/gcc/testsuite/g++.dg/lto/pr83720_0.C
+++ w/gcc/testsuite/g++.dg/lto/pr83720_0.C
@@ -48,7 +48,7 @@ public:
   k(al<void(b::ai)>);
 } d([](b::ai) {
   struct be {
-    virtual void f();
+    virtual void f(){}
   };
   struct bf;
   b::c<bf>().aj("", &be::f);