ctest: Restore support for --timeout values higher than default test timeout

Since refactoring in commit 0a5aeaf302 (cmCTestRunTest: Consolidate test
timeout selection logic, 2023-05-04, v3.27.0-rc1~120^2) we accidentally
truncate `--timeout` values to ctest's default `TimeOut`.  Fix the
logic to prefer the flag whenever the `TIMEOUT` property is not set.

In combination with the prior refactoring, this also fixes a bug that
caused `--timeout` values of 10000000 seconds or more to be ignored.

Fixes: #23979

Help/manual/ctest.1.rst

@@ -1230,7 +1230,8 @@ Configuration settings include:
 
 ``TimeOut``
   The default timeout for each test if not specified by the
-  :prop_test:`TIMEOUT` test property.
+  :prop_test:`TIMEOUT` test property or the
+  :option:`--timeout <ctest --timeout>` flag.
 
   * `CTest Script`_ variable: :variable:`CTEST_TEST_TIMEOUT`
   * :module:`CTest` module variable: ``DART_TESTING_TIMEOUT``

Source/CTest/cmCTestRunTest.cxx

@@ -768,11 +768,12 @@ bool cmCTestRunTest::ForkProcess()
       timeout = this->CTest->GetGlobalTimeout();
     }
 
-    // Check CTEST_TEST_TIMEOUT.
-    cmDuration ctestTestTimeout = this->CTest->GetTimeOut();
-    if (ctestTestTimeout > cmDuration::zero() &&
-        (!timeout || ctestTestTimeout < *timeout)) {
-      timeout = ctestTestTimeout;
+    if (!timeout) {
+      // Check CTEST_TEST_TIMEOUT.
+      cmDuration ctestTestTimeout = this->CTest->GetTimeOut();
+      if (ctestTestTimeout > cmDuration::zero()) {
+        timeout = ctestTestTimeout;
+      }
     }
   }
 

Tests/RunCMake/CTestTimeout/FlagOverridesVar-stdout.txt

@@ -0,0 +1,6 @@
+Test project [^
+]*/Tests/RunCMake/CTestTimeout/FlagOverridesVar-build
+    Start 1: TestTimeout
+1/1 Test #1: TestTimeout ......................   Passed +[1-9][0-9.]* sec
++
+100% tests passed, 0 tests failed out of 1

Tests/RunCMake/CTestTimeout/RunCMakeTest.cmake

@@ -94,3 +94,10 @@ block()
   set(CASE_CMAKELISTS_SUFFIX_CODE "set_property(TEST TestTimeout PROPERTY TIMEOUT 10)\n")
   run_ctest_timeout(PropertyOverridesVar)
 endblock()
+
+block()
+  set(TIMEOUT 4)
+  set(CASE_TEST_PREFIX_CODE "set(CTEST_TEST_TIMEOUT 2)")
+  set(CASE_CMAKELISTS_SUFFIX_CODE "set_property(TEST TestTimeout PROPERTY TIMEOUT)\n")
+  run_ctest_timeout(FlagOverridesVar --timeout 10000001)
+endblock()