Modify Qt min version to 5.9.0

Author: KangLin

CMakeLists.txt

@@ -64,7 +64,7 @@ if (NOT (Qt5_FOUND OR Qt6_FOUND))
     elseif(Qt5_FOUND)
         message("Qt5 found.")
         message(STATUS "Qt version is ${Qt5Core_VERSION}")
-        set(QT_MIN_VERSION 5.12.0)
+        set(QT_MIN_VERSION 5.9.0)
     else()
         message(FATAL_ERROR "No Qt found!")
     endif()

src/log4qt/log4qt.h

@@ -459,8 +459,8 @@
 
 #include <qglobal.h>
 
-#if QT_VERSION < QT_VERSION_CHECK(5, 12, 0)
-#   error "Log4Qt requires Qt version 5.12.0 or higher"
+#if QT_VERSION < QT_VERSION_CHECK(5, 9, 0)
+#   error "Log4Qt requires Qt version 5.9.0 or higher"
 #endif
 
 #if (defined(Q_CC_MSVC) && _MSC_VER < 1900)