Zip: Allow usage of system zlib (default if found)

Set QTC_USE_SYSTEM_ZLIB to override the default
(which is already done for our prebuilt binaries in build.py)

Fixes: QTCREATORBUG-32584
Change-Id: Ib893ee9daa24a831308dfffd6e33d6e79aac2356
Reviewed-by: Eike Ziller <eike.ziller@qt.io>
Reviewed-by: Marcus Tillmanns <marcus.tillmanns@qt.io>

src/libs/solutions/zip/CMakeLists.txt

@@ -6,12 +6,27 @@ add_qtc_library(Zip
     zipreader.h
     zipwriter.h
     zip_global.h
-    INCLUDES
-      ${CMAKE_CURRENT_LIST_DIR}/../../3rdparty/zlib/src
 )
 
+find_package(ZLIB QUIET)
+if(ZLIB_FOUND)
+  set(QTC_USE_SYSTEM_ZLIB_DEFAULT ON)
+else()
+  set(QTC_USE_SYSTEM_ZLIB_DEFAULT OFF)
+endif()
+option(QTC_USE_SYSTEM_ZLIB "Use system zlib for Zip" ${QTC_USE_SYSTEM_ZLIB_DEFAULT})
+
+if (QTC_USE_SYSTEM_ZLIB)
   extend_qtc_library(Zip
+    FEATURE_INFO "System zlib"
+    DEPENDS ZLIB::ZLIB
+  )
+else()
+  extend_qtc_library(Zip
+    FEATURE_INFO "Integrated zlib"
     SOURCES_PREFIX ${CMAKE_CURRENT_LIST_DIR}/../../3rdparty/zlib/src
+    INCLUDES
+      ${CMAKE_CURRENT_LIST_DIR}/../../3rdparty/zlib/src
     SKIP_AUTOMOC
     SOURCES
       adler32.c
@@ -41,7 +56,7 @@ extend_qtc_library(Zip
       zutil.c
       zutil.h
   )
-
   if(MSVC)
     target_compile_options(Zip PUBLIC /wd4996)
   endif()
+endif()