Have any bosses have been familiar with cmake. Help to look at. This is a bug cmake?-CodePudding

I wrote a simple Qt application, use qmake and pro, with the administration of cmake
Source files in the directory:/home/username/QtProjects/untitled
There is only one file. The main CPP, content as follows:

 
#include  
#include  

using namespace std; 

Int main (int arg c, char * * argv) 
{
QApplication app (arg c, argv); 
QWidget * w=new QWidget (); 
W - & gt; Show (); 
Return the app. The exec (); 
}

CMakeLists. TXT content is as follows:

 
Cmake_minimum_required (VERSION 2.8) 

Set (CMAKE_CXX_STANDARD 11) 
Set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fpic") 
Set (CMAKE_BUILD_TYPE "Debug") 

Set (CMAKE_PREFIX_PATH/home/username/qt/5.7/gcc_64/bin) 
Set (CMAKE_INCLUDE_CURRENT_DIR ON) 

Qt MOC # open 
Set (CMAKE_AUTOMOC ON) 
# open Qt ROC 
Set (CMAKE_AUTORCC ON) 
# open Qt UIC 
Set (CMAKE_AUTOUIC ON) 
# Qt module 
Set (QT Core Gui Widgets) 
# project name 
Project (untitled) 
# qt installation root directory 
Set (QT_BASE_DIR/home/username/qt/5.7/gcc_64) 
# header file search directory 
Include_directories (
The ${QT_BASE_DIR}/include/QtCore 
The ${QT_BASE_DIR}/include/QtGui 
The ${QT_BASE_DIR}/include/QtWidgets 
The ${QT_BASE_DIR}/include 
) 
# libraries directory 
Link_directories (
The ${QT_BASE_DIR}/lib 
) 
# add an executable program 
Add_executable (${PROJECT_NAME} ". The main CPP ") 
# specified link library 
Target_link_libraries (
The ${PROJECT_NAME} 
Qt5Core 
Qt5Gui 
Qt5Widgets 
)

The problem on the -fpic, I perform cmake command: the compilation of the program directory

 cmake/home/username/QtProjects/untitled

Executed directly make compilation, complains:

Error that no use -fpic here, but my CMakeLists. TXT clearly is garnering -fpic, oddly, if at this time, to do the same again cmake command:

 cmake/home/username/QtProjects/untitled

, compile again, there is no problem, compared before and after the differences I found the first execution cmake, in:/CMakeFiles/untitled. Dir/flags. The make file CXX_FLAGS did not take the -fpic, however the second after execution, here with the -fpic, surprised the same command twice appeared different results,

My machine is Ubuntu 16.04, apt - get install cmake version is 3.5.1 track of.
Later I manually compile installed cmake 3.16.5 did not appear this problem, know big trouble explain, this problem is cmake bug? Or my own cmakelist writing has a problem?