Add detect redhat and unknown in CMake

cmake/system.cmake

@@ -30,6 +30,10 @@ ELSE(WIN32)
                 SET(HOST_SYSTEM "debian")
             ELSEIF(LINUX_ISSUE MATCHES "Ubuntu")
                 SET(HOST_SYSTEM "ubuntu")
+            ELSEIF(LINUX_ISSUE MATCHES "Red Hat")
+                SET(HOST_SYSTEM "redhat")
+            ELSEIF(LINUX_ISSUE MATCHES "Fedora")
+                SET(HOST_SYSTEM "fedora")
             ENDIF()
         ENDIF(EXISTS "/etc/issue")
 
@@ -40,6 +44,10 @@ ELSE(WIN32)
             ENDIF()
         ENDIF(EXISTS "/etc/redhat-release")
 
+        IF(NOT HOST_SYSTEM)
+            SET(HOST_SYSTEM "unknown")
+        ENDIF()
+
     ENDIF(APPLE)
 ENDIF(WIN32)