1. If I try to build the qtquickcontrols2 module:

In file included from ../../include/QtQuickTemplates2/5.12.3/QtQuickTemplates2/private/qtquicktemplates2global_p.h:1:0,
                 from ../../include/QtQuickTemplates2/5.12.3/QtQuickTemplates2/private/../../../../../../qtquickcontrols2/src/quicktemplates2/qquickcontrol_p.h:54,
                 from ../../include/QtQuickTemplates2/5.12.3/QtQuickTemplates2/private/qquickcontrol_p.h:1,
                 from /home/spyros/qt5/qtquickcontrols2/src/quicktemplates2/qquickbusyindicator_p.h:51,
                 from /home/spyros/qt5/qtquickcontrols2/src/quicktemplates2/qquickbusyindicator.cpp:37:
../../include/QtQuickTemplates2/5.12.3/QtQuickTemplates2/private/../../../../../../qtquickcontrols2/src/quicktemplates2/qtquicktemplates2global_p.h:52:10: fatal error: QtQml/private/qqmlglobal_p.h: No such file or directory
 #include <QtQml/private/qqmlglobal_p.h>
          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from ../../include/QtQuickTemplates2/5.12.3/QtQuickTemplates2/private/qtquicktemplates2global_p.h:1:0,
                 from ../../include/QtQuickTemplates2/5.12.3/QtQuickTemplates2/private/../../../../../../qtquickcontrols2/src/quicktemplates2/qquickcontrol_p.h:54,
                 from ../../include/QtQuickTemplates2/5.12.3/QtQuickTemplates2/private/qquickcontrol_p.h:1,
                 from /home/spyros/qt5/qtquickcontrols2/src/quicktemplates2/qquickabstractbutton_p.h:51,
                 from /home/spyros/qt5/qtquickcontrols2/src/quicktemplates2/qquickabstractbutton.cpp:37:
../../include/QtQuickTemplates2/5.12.3/QtQuickTemplates2/private/../../../../../../qtquickcontrols2/src/quicktemplates2/qtquicktemplates2global_p.h:52:10: fatal error: QtQml/private/qqmlglobal_p.h: No such file or directory
 #include <QtQml/private/qqmlglobal_p.h>
          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from ../../include/QtQuickTemplates2/5.12.3/QtQuickTemplates2/private/qtquicktemplates2global_p.h:1:0,
                 from ../../include/QtQuickTemplates2/5.12.3/QtQuickTemplates2/private/../../../../../../qtquickcontrols2/src/quicktemplates2/qquickcontrol_p.h:54,
                 from ../../include/QtQuickTemplates2/5.12.3/QtQuickTemplates2/private/qquickcontrol_p.h:1,
                 from ../../include/QtQuickTemplates2/5.12.3/QtQuickTemplates2/private/../../../../../../qtquickcontrols2/src/quicktemplates2/qquickabstractbutton_p.h:51,
                 from ../../include/QtQuickTemplates2/5.12.3/QtQuickTemplates2/private/qquickabstractbutton_p.h:1,
                 from /home/spyros/qt5/qtquickcontrols2/src/quicktemplates2/qquickbutton_p.h:51,
                 from /home/spyros/qt5/qtquickcontrols2/src/quicktemplates2/qquickbutton.cpp:37:
../../include/QtQuickTemplates2/5.12.3/QtQuickTemplates2/private/../../../../../../qtquickcontrols2/src/quicktemplates2/qtquicktemplates2global_p.h:52:10: fatal error: QtQml/private/qqmlglobal_p.h: No such file or directory
 #include <QtQml/private/qqmlglobal_p.h>
          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
compilation terminated.
compilation terminated.
compilation terminated.
Makefile:9664: recipe for target '.obj/qquickabstractbutton.o' failed
Makefile:10141: recipe for target '.obj/qquickbusyindicator.o' failed
Makefile:10278: recipe for target '.obj/qquickbutton.o' failed
make[2]: *** [.obj/qquickabstractbutton.o] Error 1
make[2]: *** Waiting for unfinished jobs....
make[2]: *** [.obj/qquickbusyindicator.o] Error 1
make[2]: *** [.obj/qquickbutton.o] Error 1
In file included from ../../include/QtQuickTemplates2/5.12.3/QtQuickTemplates2/private/qtquicktemplates2global_p.h:1:0,
                 from ../../include/QtQuickTemplates2/5.12.3/QtQuickTemplates2/private/../../../../../../qtquickcontrols2/src/quicktemplates2/qquickcontrol_p.h:54,
                 from ../../include/QtQuickTemplates2/5.12.3/QtQuickTemplates2/private/qquickcontrol_p.h:1,
                 from /home/spyros/qt5/qtquickcontrols2/src/quicktemplates2/qquickcombobox_p.h:51,
                 from /home/spyros/qt5/qtquickcontrols2/src/quicktemplates2/qquickcombobox.cpp:37:
../../include/QtQuickTemplates2/5.12.3/QtQuickTemplates2/private/../../../../../../qtquickcontrols2/src/quicktemplates2/qtquicktemplates2global_p.h:52:10: fatal error: QtQml/private/qqmlglobal_p.h: No such file or directory
 #include <QtQml/private/qqmlglobal_p.h>
          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
compilation terminated.

**************************

2. If I try to build only the calendar:

WARNING: DESTDIR: Cannot access directory '/qml/Qt/labs/calendar'
WARNING: qmlcachegen: Cannot access directory '../../../../../../../qml/Qt/labs/calendar'
WARNING: qmlcachegen: Cannot access directory '../../../../../../../qml/Qt/labs/calendar'
WARNING: qmlcachegen: Cannot access directory '../../../../../../../qml/Qt/labs/calendar'
WARNING: copy_qmldir2build: Cannot access directory '/qml/Qt/labs/calendar'
WARNING: copy_qmldir2build: Cannot access directory '/qml/Qt/labs/calendar'
20:54:49: The process "/home/spyros/Qt/5.12.2/gcc_64/bin/qmake" exited normally.
20:54:49: Starting: "/usr/bin/make" -f /home/spyros/qt5/qtquickcontrols2/src/imports/build-calendar-Desktop_Qt_5_12_2_GCC_64bit-Debug/Makefile qmake_all
make: Nothing to be done for 'qmake_all'.
20:54:49: The process "/usr/bin/make" exited normally.
20:54:49: Starting: "/usr/bin/make" -j4
/home/spyros/qt5/qtquickcontrols2/src/imports/build-calendar-Desktop_Qt_5_12_2_GCC_64bit-Debug/qmlcachegen_wrapper.sh -o ../../../../../../../qml/Qt/labs/calendar/DayOfWeekRow.qmlc ../calendar/DayOfWeekRow.qml
/home/spyros/qt5/qtquickcontrols2/src/imports/build-calendar-Desktop_Qt_5_12_2_GCC_64bit-Debug/qmlcachegen_wrapper.sh -o ../../../../../../../qml/Qt/labs/calendar/MonthGrid.qmlc ../calendar/MonthGrid.qml
/home/spyros/qt5/qtquickcontrols2/src/imports/build-calendar-Desktop_Qt_5_12_2_GCC_64bit-Debug/qmlcachegen_wrapper.sh -o ../../../../../../../qml/Qt/labs/calendar/WeekNumberColumn.qmlc ../calendar/WeekNumberColumn.qml
/home/spyros/Qt/5.12.2/gcc_64/bin/qmake -install qinstall ../calendar/qmldir /qml/Qt/labs/calendar/qmldir
Error copying ../calendar/qmldir to /qml/Qt/labs/calendar/qmldir: Cannot create /qml/Qt/labs/calendar/qmldir for output
Makefile:1362: recipe for target '/qml/Qt/labs/calendar/qmldir' failed
make: *** [/qml/Qt/labs/calendar/qmldir] Error 3
make: *** Waiting for unfinished jobs....
Error compiling qml file: No such file or directory
Error compiling qml file: No such file or directory
Error compiling qml file: No such file or directory
Makefile:821: recipe for target '../../../../../../../qml/Qt/labs/calendar/MonthGrid.qmlc' failed
make: *** [../../../../../../../qml/Qt/labs/calendar/MonthGrid.qmlc] Error 1
make: *** [../../../../../../../qml/Qt/labs/calendar/DayOfWeekRow.qmlc] Error 1
make: *** [../../../../../../../qml/Qt/labs/calendar/WeekNumberColumn.qmlc] Error 1
Makefile:818: recipe for target '../../../../../../../qml/Qt/labs/calendar/DayOfWeekRow.qmlc' failed
Makefile:824: recipe for target '../../../../../../../qml/Qt/labs/calendar/WeekNumberColumn.qmlc' failed
20:54:50: The process "/usr/bin/make" exited with code 2.
Error while building/deploying project calendar (kit: Desktop Qt 5.12.2 GCC 64bit)
When executing step "Make"
20:54:50: Elapsed time: 00:01.