Unit test framwork: use references when catching exceptions

GCC 8 warns about catching by value; this was not caught in the earlier cleanup
as it did not include unit tests.

Author: tautschnig

jbmc/unit/java_bytecode/java_types/erase_type_arguments.cpp

@@ -63,6 +63,6 @@ SCENARIO("erase_type_arguments", "[core][java_types]")
     REQUIRE_THROWS_AS(
       erase_type_arguments(
         "testClassName<testTypeArgument1<testTypeArgument2>"),
-      unsupported_java_class_signature_exceptiont &);
+      unsupported_java_class_signature_exceptiont);
   }
 }

unit/testing-utils/catch.hpp

@@ -2245,7 +2245,7 @@ namespace Catch {
                 static_cast<void>(expr); \
                 __catchResult.captureResult( Catch::ResultWas::DidntThrowException ); \
             } \
-            catch( exceptionType ) { \
+            catch( const exceptionType & ) { \
                 __catchResult.captureResult( Catch::ResultWas::Ok ); \
             } \
             catch( ... ) { \