Fix build with icu >=75

Index: CMakeLists.txt
--- CMakeLists.txt.orig
+++ CMakeLists.txt
@@ -1,10 +1,12 @@
-cmake_minimum_required(VERSION 3.0 FATAL_ERROR)
+cmake_minimum_required(VERSION 3.16)
 find_package(ECM 1.8.0 REQUIRED NO_MODULE)
 set(CMAKE_MODULE_PATH ${CMAKE_SOURCE_DIR}/cmake/modules ${ECM_MODULE_PATH} ${ECM_KDE_MODULE_DIR})
 include(SetKDbCMakePolicies NO_POLICY_SCOPE)
 
 project(KDb VERSION 3.2.0) # Update this
 
+set(CMAKE_CXX_STANDARD 17)
+
 include(KDbAddTests)
 include(KDbAddExamples)
 kdb_add_tests(OFF)
@@ -61,4 +63,4 @@ if (IS_DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}/po")
     ecm_install_po_files_as_qm(po)
 endif()
 
-feature_summary(WHAT ALL FATAL_ON_MISSING_REQUIRED_PACKAGES)
+feature_summary(WHAT ALL)
