GoogleTest: Add test for missing test executable

Add a test to verify expected behavior when a test executable on which
gtest_discover_tests is invoked was not built. (The test for the newly
added timeout conveniently sets up this situation, so this new test was
almost trivial to add.)

Tests/RunCMake/GoogleTest/GoogleTest-test-missing-result.txt

@@ -0,0 +1 @@
+[^0]

Tests/RunCMake/GoogleTest/GoogleTest-test-missing-stderr.txt

@@ -0,0 +1,2 @@
+Unable to find executable: timeout_test_NOT_BUILT
+Errors while running CTest

Tests/RunCMake/GoogleTest/RunCMakeTest.cmake

@@ -41,6 +41,13 @@ function(run_GoogleTest)
     -L TEST2
     --no-label-summary
   )
+
+  run_cmake_command(GoogleTest-test-missing
+    ${CMAKE_CTEST_COMMAND}
+    -C Debug
+    -R timeout
+    --no-label-summary
+  )
 endfunction()
 
 run_GoogleTest()