Prevent CMake 2.8 tests failing for unused variable (causing millisec to be dropped from stat calls) (#28573)

* Prevent CMake 2.8 tests failing for unused variable

* Make sterror_r test fail as it should

* Reenable tests

Author: danmoseley

src/Native/Unix/configure.cmake

@@ -28,7 +28,9 @@ else ()
 endif ()
 
 # We compile with -Werror, so we need to make sure these code fragments compile without warnings.
-set(CMAKE_REQUIRED_FLAGS -Werror)
+# Older CMake versions (3.8) do not assign the result of their tests, causing unused-value errors
+# which are not distinguished from the test failing. So no error for that one.
+set(CMAKE_REQUIRED_FLAGS "-Werror -Wno-error=unused-value")
 
 # This compiler warning will fail code as innocuous as:
 # static pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;
@@ -229,7 +231,7 @@ check_c_source_compiles(
     int main()
     {
         char buffer[1];
-        char* c = strerror_r(0, buffer, 0);
+        char c = *strerror_r(0, buffer, 0);
         return 0;
     }
     "

src/System.IO.FileSystem/tests/Base/BaseGetSetTimes.cs

@@ -86,8 +86,8 @@ public void TimesIncludeMillisecondPart_Linux()
                     DateTime time = function.Getter(item);
                     msec = time.Millisecond;
 
-                    //if (msec != 0)
-                    //    break;
+                    if (msec != 0)
+                        break;
 
                     // This case should only happen 1/1000 times, unless the OS/Filesystem does
                     // not support millisecond granularity.
@@ -98,14 +98,12 @@ public void TimesIncludeMillisecondPart_Linux()
                     // If it's the OS/Filesystem often returns 0 for the millisecond part, this may
                     // help prove it. This should only be written 1/1000 runs, unless the test is going to
                     // fail.
-                    //Console.WriteLine($"TimesIncludeMillisecondPart got a file time of {time.ToString("o")}");
                     Console.WriteLine($"## TimesIncludeMillisecondPart got a file time of {time.ToString("o")} on {driveFormat}");
 
                     item = GetExistingItem(); // try a new file/directory
                 }
 
-                // Temporarily disabled while investigating failures in #27662
-                // Assert.NotEqual(0, msec);
+                Assert.NotEqual(0, msec);
             });
         }
 
@@ -131,11 +129,6 @@ public void TimesIncludeMillisecondPart_Windows()
                     // If it's 1/1000, or low granularity, this may help:
                     Thread.Sleep(1234);
 
-                    // If it's the OS/Filesystem often returns 0 for the millisecond part, this may
-                    // help prove it. This should only be written 1/1000 runs, unless the test is going to
-                    // fail.
-                    Console.WriteLine($"TimesIncludeMillisecondPart got a file time of {time.ToString("o")}");
-
                     item = GetExistingItem(); // try a new file/directory
                 }