Test CHECK_(C|CXX)_COMPILER_FLAG macros

This teaches the TryCompile test to check that the compiler flag check
macros correctly reject a bad flag.  See issue #9516.

Tests/TryCompile/CMakeLists.txt

@@ -200,4 +200,12 @@ TEST_ASSERT(CXX_BUILD_SHOULD_WORK "CHECK_CXX_SOURCE_COMPILES() failed")
 TEST_FAIL(CXX_RUN_SHOULD_FAIL "CHECK_CXX_SOURCE_RUNS() succeeded, but should have failed")
 TEST_ASSERT(CXX_RUN_SHOULD_WORK "CHECK_CXX_SOURCE_RUNS() failed")
 
-
+UNSET(C_BOGUS_FLAG CACHE)
+INCLUDE(CheckCCompilerFlag)
+CHECK_C_COMPILER_FLAG(-_this_is_not_a_flag_ C_BOGUS_FLAG)
+TEST_FAIL(C_BOGUS_FLAG "CHECK_C_COMPILER_FLAG() succeeded, but should have failed")
+
+UNSET(CXX_BOGUS_FLAG CACHE)
+INCLUDE(CheckCXXCompilerFlag)
+CHECK_CXX_COMPILER_FLAG(-_this_is_not_a_flag_ CXX_BOGUS_FLAG)
+TEST_FAIL(CXX_BOGUS_FLAG "CHECK_CXX_COMPILER_FLAG() succeeded, but should have failed")