Building problem with cmake

[Furret]

Hi, everyone. I have a weird building problem.

In my project, there is a sub project which is using std::thread and builds with cmake.
The CMakeList.txt is like this:

cmake_minimum_required(VERSION 3.2)
project(integrated_calibtool)
message(STATUS ${CMAKE_CXX_FLAGS})
add_compile_options(-std=c++17 -pthread)

find_package(jsoncpp REQUIRED)
find_package(OpenCV REQUIRED)
find_package(PCL 1.9 REQUIRED)
find_package(Boost COMPONENTS thread system REQUIRED)

set(THREADS_PREFER_PTHREAD_FLAG ON)
find_package(Threads REQUIRED)
include_directories(
  ${EIGEN3_INCLUDE_DIR}
  ${PCL_INCLUDE_DIRS}
  ${OpenCV_INCLUDE_DIR}
  ${Boost_INCLUDE_DIR}
)

link_directories(${PCL_LIBRARY_DIRS})
add_definitions(${PCL_DEFINITIONS})

add_executable(exe1 ~~~)
target_link_libraries(exe1 ${OpenCV_LIBS})

add_executable(exe2 ~~~)
target_link_libraries(exe2 ${OpenCV_LIBS} jsoncpp pthread)

add_executable(exe3 ~~~)
target_link_libraries(exe3 ${OpenCV_LIBS})

add_executable(exe4 ~~~)
target_link_libraries(exe4 ${PCL_LIBRARIES})

add_executable(exe5 ~~~)
target_link_libraries(exe5 pthread)

add_library(libname STATIC 
	~~~
)

target_link_libraries(libname 
	PUBLIC ${OpenCV_LIBS}
	PUBLIC ${PCL_LIBRARIES}
	PUBLIC Threads::Threads
)

And the parent qt project cmakelist is something like this:

cmake_minimum_required(VERSION 3.5)

project(SerialManager VERSION 0.1 LANGUAGES CXX)

set(CMAKE_PREFIX_PATH /home/mtech/ExternalGitPackages/Qt/5.15.2/gcc_64)
set(CMAKE_INCLUDE_CURRENT_DIR ON)

set(CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/bin)
set(CMAKE_LIBRARY_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/bin)
set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/bin)

set(CMAKE_AUTOUIC ON)
set(CMAKE_AUTOMOC ON)
set(CMAKE_AUTORCC ON)
set(CMAKE_AUTOUIC_SEARCH_PATHS ~~~)

set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_STANDARD_REQUIRED ON)
set(THREADS_PREFER_PTHREAD_FLAG ON)

find_package(OpenCV REQUIRED)
find_package(Threads REQUIRED)

find_package(QT NAMES Qt6 Qt5 REQUIRED COMPONENTS Widgets)
find_package(Qt${QT_VERSION_MAJOR} REQUIRED COMPONENTS Widgets)
find_package(Qt5Charts)



set(PROJECT_SOURCES
        ~~~
)

add_subdirectory(subproject)

add_executable(${PROJECT_NAME}
            ${PROJECT_SOURCES}
        )
#target_include_directories(${PROJECT_NAME}
#    PUBLIC integrated_calibration_tool
#)

#add_library(integrated_calibration_tool)
include_directories(${CMAKE_SOURCE_DIR}/integrated_calibration_tool)

target_link_libraries(${PROJECT_NAME}
    PUBLIC ${OpenCV_LIBS}
    PRIVATE Qt${QT_VERSION_MAJOR}::Widgets
    PRIVATE Qt${QT_VERSION_MAJOR}::Charts
    libmade
    PRIVATE Threads::Threads
)

set_target_properties(${PROJECT_NAME} PROPERTIES
    MACOSX_BUNDLE_GUI_IDENTIFIER my.example.com
    MACOSX_BUNDLE_BUNDLE_VERSION ${PROJECT_VERSION}
    MACOSX_BUNDLE_SHORT_VERSION_STRING ${PROJECT_VERSION_MAJOR}.${PROJECT_VERSION_MINOR}
    MACOSX_BUNDLE TRUE
    WIN32_EXECUTABLE TRUE
)

The problem is, I can completely build my qt project with cmake, but cannot with qtCreator.
I made a folder "build" where

build-Qtproject-Desktop_Qt_5_15_2_GCC_64bit-Debug and
Qtproject

both exists, and

cd build
cmake ../Qtproject
make

, no problem.

On the otherside, Qt Creator keeps alerting me that
/usr/include/c++/9/thread:126: error: undefined reference to `pthread_create'

Actually, this error message pops up when I use cmake by explicitly telling the source and build location like this:

mkdir build
cmake -S Qtproject/ -B build/

What is the thing that I'm missing??

Thanks.

[Axel Spoerl]

Have a look at this.
GCC-9 should work with the latest Qt 5.15-lts on Ubuntu 18.04 and 20.04.
All other Linuxes on 5.15 prefer GCC-5, or GCC-10 and above.
Qt 5.15.2, however, is not the latest LTS release.
Isn't Qt 6 an option?