Fix build with icu >=75

Index: CMakeLists.txt
--- CMakeLists.txt.orig
+++ CMakeLists.txt
@@ -5,6 +5,8 @@ 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)
