Adapt build system for building against qt6

(cherry picked from commit 651793a62f798c496f1934cd3278da26b6d62c33)

CMakeLists.txt

@@ -45,8 +45,10 @@ ecm_setup_version(PROJECT VARIABLE_PREFIX KSMTP
 
 
 ############ Find packages ############
-find_package(Qt5Network ${QT_REQUIRED_VERSION} REQUIRED)
-
+find_package(Qt${QT_MAJOR_VERSION}Network ${QT_REQUIRED_VERSION} REQUIRED)
+if (QT_MAJOR_VERSION STREQUAL "6")
+    find_package(Qt6Core5Compat)
+endif()
 find_package(KF5CoreAddons ${KF5_MIN_VERSION} CONFIG REQUIRED)
 find_package(KF5I18n ${KF5_MIN_VERSION} CONFIG REQUIRED)
 find_package(KF5KIO ${KF5_MIN_VERSION} CONFIG REQUIRED)

autotests/CMakeLists.txt

 # SPDX-FileCopyrightText: none
 # SPDX-License-Identifier: BSD-3-Clause
 include(ECMAddTests)
-find_package(Qt5Test ${QT_REQUIRED_VERSION} REQUIRED)
+find_package(Qt${QT_MAJOR_VERSION}Test ${QT_REQUIRED_VERSION} REQUIRED)
 
 ecm_add_test(smtptest.cpp fakeserver.cpp smtptest.h fakeserver.h
-    LINK_LIBRARIES KPimSMTP Qt::Test Qt::Network
+    LINK_LIBRARIES KPimSMTP Qt${QT_MAJOR_VERSION}::Test Qt${QT_MAJOR_VERSION}::Network
     TEST_NAME smtptest
 )

src/CMakeLists.txt

@@ -43,7 +43,7 @@ PUBLIC
 PRIVATE
     KF5::I18n
     KF5::KIOCore
-    Qt::Network
+    Qt${QT_MAJOR_VERSION}::Network
     Sasl2::Sasl2
     ${extra_LIBS}
 )

tests/CMakeLists.txt

 # SPDX-FileCopyrightText: none
 # SPDX-License-Identifier: BSD-3-Clause
 add_executable(logintest logintest.cpp)
-target_link_libraries(logintest KPimSMTP Qt::Core KF5::KIOWidgets)
+target_link_libraries(logintest KPimSMTP Qt${QT_MAJOR_VERSION}::Core KF5::KIOWidgets)