Utils: Make sure we only use fdatasync() on systems that have it.

Change-Id: I7260c05081942acd5ecd7c66e864d4efc5041add
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>

src/libs/utils/savefile.cpp

@@ -102,10 +102,10 @@ bool SaveFile::commit()
     }
 #ifdef Q_OS_WIN
     FlushFileBuffers(reinterpret_cast<HANDLE>(handle()));
-#elif defined(Q_OS_MAC)
-    fsync(handle());
-#else
+#elif _POSIX_SYNCHRONIZED_IO > 0
     fdatasync(handle());
+#else
+    fsync(handle());
 #endif
     close();
     if (error() != NoError) {