cmake: raise minimal cmake version to 3.5 and use its features

CMakeLists.txt

@@ -1,5 +1,5 @@
-cmake_minimum_required(VERSION 3.2)
-cmake_policy(VERSION 3.2)
+cmake_minimum_required(VERSION 3.5)
+cmake_policy(VERSION 3.5)
 
 project(qBittorrent VERSION 3.4.0.0)
 

src/base/CMakeLists.txt

@@ -1,5 +1,4 @@
 find_package(ZLIB REQUIRED)
-include_directories(SYSTEM ${ZLIB_INCLUDE_DIRS})
 
 set(QBT_BASE_HEADERS
 bittorrent/cachestatus.h
@@ -113,7 +112,7 @@ tristatebool.cpp
 )
 
 add_library(qbt_base STATIC ${QBT_BASE_HEADERS} ${QBT_BASE_SOURCES})
-target_link_libraries(qbt_base ${ZLIB_LIBRARIES} LibtorrentRasterbar::LibTorrent)
+target_link_libraries(qbt_base ZLIB::ZLIB LibtorrentRasterbar::LibTorrent)
 target_link_qt_components(qbt_base Core Network Xml)
 if (QT4_FOUND)
     if (GUI)