Tests: Enable missing Objective C/C++ tests

Some test cases added by commit 80f120a85f (Languages: Add support for
Objective-C, 2019-09-13, v3.16.0-rc1~44^2~3) have never actually been
run because the condition to enable them is never true.  Fix the
condition and fix the tests to pass.

Tests/CMakeOnly/CMakeLists.txt

@@ -31,12 +31,9 @@ add_CMakeOnly_test(CheckStructHasMember)
 add_CMakeOnly_test(CompilerIdC)
 add_CMakeOnly_test(CompilerIdCXX)
 
-if(CMAKE_OBJC_COMPILER)
+if (APPLE AND CMAKE_C_COMPILER_ID MATCHES "Clang|GNU")
   add_CMakeOnly_test(CompilerIdOBJC)
   add_CMakeOnly_test(CheckOBJCCompilerFlag)
-endif()
-
-if(CMAKE_OBJCXX_COMPILER)
   add_CMakeOnly_test(CompilerIdOBJCXX)
   add_CMakeOnly_test(CheckOBJCXXCompilerFlag)
 endif()

Tests/CMakeOnly/CheckOBJCCompilerFlag/CMakeLists.txt

@@ -1,17 +1,7 @@
-cmake_minimum_required(VERSION 2.8.12)
-
-project(CheckOBJCCompilerFlag)
-
+cmake_minimum_required(VERSION 3.16)
+project(CheckOBJCCompilerFlag OBJC)
 include(CheckOBJCCompilerFlag)
-
-if(CMAKE_COMPILER_IS_GNUOBJC)
-  set(COMPILER_FLAG -fobjc-direct-dispatch)
-else()
-  set(COMPILER_FLAG -fobjc-gc)
-endif()
-
-CHECK_OBJC_COMPILER_FLAGS(${COMPILER_FLAG} HAS_COMPILER_FLAG)
-
+check_objc_compiler_flag(-DFOO HAS_COMPILER_FLAG)
 if(NOT HAS_COMPILER_FLAG)
   message(SEND_ERROR "Test fail: HAS_COMPILER_FLAG: ${COMPILER_FLAG}")
-endif
+endif()

Tests/CMakeOnly/CheckOBJCXXCompilerFlag/CMakeLists.txt

@@ -1,17 +1,7 @@
-cmake_minimum_required(VERSION 2.8.12)
-
-project(CheckOBJCXXCompilerFlag)
-
+cmake_minimum_required(VERSION 3.16)
+project(CheckOBJCXXCompilerFlag OBJCXX)
 include(CheckOBJCXXCompilerFlag)
-
-if(CMAKE_COMPILER_IS_GNUOBJCXX)
-  set(COMPILER_FLAG -fobjc-direct-dispatch)
-else()
-  set(COMPILER_FLAG -fobjc-gc)
-endif()
-
-CHECK_OBJCXX_COMPILER_FLAGS(${COMPILER_FLAG} HAS_COMPILER_FLAG)
-
+check_objcxx_compiler_flag(-DFOO HAS_COMPILER_FLAG)
 if(NOT HAS_COMPILER_FLAG)
   message(SEND_ERROR "Test fail: HAS_COMPILER_FLAG: ${COMPILER_FLAG}")
 endif()