Replace -fPIC with -fpic - c++

Question

When using Qt CMake automatically adds the -fPIC flag to compile options. I want to use -fpic, so I went through all Cmake variables and replaced -fPIC with -fpic.
cmake_minimum_required(VERSION 3.5)
project(sss)
find_package(Qt5 REQUIRED COMPONENTS Core Sql)
get_cmake_property(_variableNames VARIABLES)
foreach (_variableName ${_variableNames})
if (NOT "${${_variableName}}" STREQUAL "")
string(REPLACE "-fPIC" "-fpic" ${_variableName} ${${_variableName}})
string(REPLACE "-fPIE" "-fpie" ${_variableName} ${${_variableName}})
endif()
#message(STATUS "${_variableName}=${${_variableName}}")
endforeach()
set(CMAKE_CXX_FLAGS "-fpie")
set(CMAKE_EXE_LINKER_FLAGS "-fpie -pie")
add_executable(sss main.cpp)
target_link_libraries(sss Qt5::Core Qt5::Sql)
main.cpp contains
#include <QSqlDatabase>
int main(){
QSqlDatabase::addDatabase("QPSQL");
}
Unfortunately CMake still adds the -fPIC flag, althoguh the listed variables does not contain it:
Building CXX object CMakeFiles/sss.dir/main.cpp.o
/usr/bin/c++ -DQT_CORE_LIB -DQT_NO_DEBUG -DQT_SQL_LIB -isystem /usr/include/x86_64-linux-gnu/qt5 -isystem /usr/include/x86_64-linux-gnu/qt5/QtCore -isystem /usr/lib/x86_64-linux-gnu/qt5/mkspecs/linux-g++-64 -isystem /usr/include/x86_64-linux-gnu/qt5/QtSql -fPIC -o CMakeFiles/sss.dir/main.cpp.o -c src/main.cpp
How can I replace -fPIC with -fpic?

Answer 1

Turning my comment into an answer
Your code overwrites CMake global variables like CMAKE_CXX_COMPILE_OPTIONS_PIC or CMAKE_CXX_COMPILE_OPTIONS_PIE.
But Qt brings its own -fPIC option through target properties. The Qt5::Core target does have INTERFACE_COMPILE_OPTIONS set to -fPIC (see e.g. here).
Try overwriting the target properties by adding
set_property(TARGET Qt5::Core PROPERTY INTERFACE_COMPILE_OPTIONS "-fpic")
after your find_package(Qt5 ...) call.