Fix different operator<< overload sets used for SFINAE and insertion

include/internal/catch_common.h

@@ -22,6 +22,10 @@
 #include <string>
 #include <cstdint>
 
+// We need a dummy global operator<< so we can bring it into Catch namespace later
+struct Catch_global_namespace_dummy {};
+std::ostream& operator<<(std::ostream&, Catch_global_namespace_dummy);
+
 namespace Catch {
 
     struct CaseSensitive { enum Choice {
@@ -63,6 +67,11 @@ namespace Catch {
 
     std::ostream& operator << ( std::ostream& os, SourceLineInfo const& info );
 
+    // Bring in operator<< from global namespace into Catch namespace
+    // This is necessary because the overload of operator<< above makes
+    // lookup stop at namespace Catch
+    using ::operator<<;
+
     // Use this in variadic streaming macros to allow
     //    >> +StreamEndStop
     // as well as