Turn off additional deprecation warnings for GCC.

In follow up from the conversation in #1269, this adds the
`-Wno-deprecate-declarations` flag to unit tests to allow them to
test deprecated APIs without all the noisy compiler warnings.
This also refactors the setting of build properties for test targets
to use `target_<...>` commands instead of `set_target_properties()`.

test/CMakeLists.txt

@@ -96,22 +96,21 @@ foreach(file ${files})
     string(REGEX REPLACE "unit-([^$]+)" "test-\\1" testcase ${file_basename})
 
     add_executable(${testcase} $<TARGET_OBJECTS:catch_main> ${file})
-    set_target_properties(${testcase} PROPERTIES
-        COMPILE_DEFINITIONS "$<$<CXX_COMPILER_ID:MSVC>:_SCL_SECURE_NO_WARNINGS>"
-        COMPILE_OPTIONS "$<$<CXX_COMPILER_ID:MSVC>:/EHsc;$<$<CONFIG:Release>:/Od>>"
+    target_compile_definitions(${testcase} PRIVATE
+      CATCH_CONFIG_FAST_COMPILE
+      $<$<CXX_COMPILER_ID:MSVC>:_SCL_SECURE_NO_WARNINGS>
+    )
+    target_compile_options(${testcase} PRIVATE
+        $<$<CXX_COMPILER_ID:MSVC>:/EHsc;$<$<CONFIG:Release>:/Od>>
+        $<$<NOT:$<CXX_COMPILER_ID:MSVC>>:-Wno-deprecated;-Wno-float-equal>
+        $<$<CXX_COMPILER_ID:GNU>:-Wno-deprecated-declarations>
+    )
+    target_include_directories(${testcase} PRIVATE
+        thirdparty/catch
+        thirdparty/fifo_map
     )
-
-    target_compile_definitions(${testcase} PRIVATE CATCH_CONFIG_FAST_COMPILE)
-    target_compile_features(${testcase} PRIVATE cxx_std_11)
-    target_include_directories(${testcase} PRIVATE "thirdparty/catch")
-    target_include_directories(${testcase} PRIVATE "thirdparty/fifo_map")
-    target_include_directories(${testcase} PRIVATE ${NLOHMANN_JSON_INCLUDE_BUILD_DIR})
     target_link_libraries(${testcase} ${NLOHMANN_JSON_TARGET_NAME})
 
-    if(NOT MSVC)
-        set_target_properties(${testcase} PROPERTIES COMPILE_FLAGS "${CMAKE_CXX_FLAGS} -Wno-deprecated -Wno-float-equal")
-    endif()
-
     add_test(NAME "${testcase}_default"
       COMMAND ${testcase} ${CATCH_TEST_FILTER}
       WORKING_DIRECTORY ${CMAKE_SOURCE_DIR}
@@ -131,5 +130,4 @@ foreach(file ${files})
         )
         set_tests_properties("${testcase}_valgrind" PROPERTIES LABELS "valgrind")
     endif()
-
 endforeach()