tests usage of explicit in a friend decl

From-SVN: r23350

gcc/testsuite/g++.old-deja/g++.brendan/explicit1.C

@@ -0,0 +1,6 @@
+// Build don't link: 
+
+// $7.1.2 disallows explicit on anything but declarations of
+// constructors ... including friends.
+class foo { public: foo(); };
+class bar { public: friend explicit foo::foo(); };