Tests: require C++11 for some protobuf tests

Newer versions of Protobuf require C++11, which is reflected in the imported
target created by FindProtobuf. Manually set this for all tests that only use
the variables.

Tests/FindProtobuf/Test/CMakeLists.txt

@@ -29,6 +29,7 @@ add_test(NAME test_tgt_protoc COMMAND test_tgt_protoc)
 add_executable(test_var_protoc main-protoc.cxx)
 target_include_directories(test_var_protoc PRIVATE ${Protobuf_INCLUDE_DIRS})
 target_link_libraries(test_var_protoc PRIVATE ${Protobuf_PROTOC_LIBRARIES})
+target_compile_features(test_var_protoc PRIVATE cxx_std_11)
 add_test(NAME test_var_protoc COMMAND test_var_protoc)
 
 add_test(NAME test_tgt_protoc_version COMMAND protobuf::protoc --version)
@@ -37,14 +38,17 @@ set(Protobuf_IMPORT_DIRS ${Protobuf_INCLUDE_DIRS})
 PROTOBUF_GENERATE_CPP(PROTO_SRC PROTO_HEADER msgs/example.proto)
 PROTOBUF_GENERATE_CPP(DESC_PROTO_SRC DESC_PROTO_HEADER DESCRIPTORS DESC_PROTO_DESC msgs/example_desc.proto)
 add_library(msgs ${PROTO_SRC} ${PROTO_HEADER})
+target_compile_features(msgs PRIVATE cxx_std_11)
 
 add_executable(test_generate main-generate.cxx ${PROTO_SRC})
 target_include_directories(test_generate PRIVATE ${CMAKE_CURRENT_BINARY_DIR})
 target_link_libraries(test_generate msgs ${Protobuf_LIBRARIES})
+target_compile_features(test_generate PRIVATE cxx_std_11)
 add_test(NAME test_generate COMMAND test_generate)
 
 add_executable(test_desc main-desc.cxx ${DESC_PROTO_SRC})
 target_compile_features(test_desc PRIVATE cxx_std_11)
 target_include_directories(test_desc PRIVATE ${CMAKE_CURRENT_BINARY_DIR})
 target_link_libraries(test_desc msgs ${Protobuf_LIBRARIES})
+target_compile_features(test_desc PRIVATE cxx_std_11)
 add_test(NAME test_desc COMMAND test_desc ${DESC_PROTO_DESC})