Build zlib if needed

CMakeLists.txt

@@ -204,7 +204,10 @@ if(MSVC)
 	endforeach()
 endif()
 
-find_package(ZLIB REQUIRED)
+find_package(ZLIB QUIET)
+if(NOT ZLIB_FOUND)
+	add_subdirectory(external/zlib EXCLUDE_FROM_ALL)
+endif()
 
 find_package(Eigen3 QUIET)
 
@@ -334,7 +337,8 @@ target_include_directories(cifpp
 	"${BOOST_REGEX_INCLUDE_DIR}"
 )
 
-target_link_libraries(cifpp PUBLIC Threads::Threads ZLIB::ZLIB ${CIFPP_REQUIRED_LIBRARIES})
+target_link_libraries(cifpp PUBLIC Threads::Threads  ${CIFPP_REQUIRED_LIBRARIES})
+target_link_libraries(cifpp PRIVATE $<BUILD_INTERFACE:ZLIB::ZLIB>)
 
 if(CMAKE_CXX_COMPILER_ID STREQUAL "AppleClang")
 	target_link_options(cifpp PRIVATE -undefined dynamic_lookup)

external/zlib/CMakeLists.txt

+cmake_minimum_required(VERSION 3.16)
+
+project(private-static-zlib LANGUAGES C)
+
+include(FetchContent)
+
+FetchContent_Declare(
+	zlib
+	GIT_REPOSITORY https://github.com/madler/zlib
+	GIT_TAG v1.3
+)
+
+FetchContent_Populate(zlib)
+
+add_library(zlibstatic STATIC
+	${zlib_SOURCE_DIR}/adler32.c
+	${zlib_SOURCE_DIR}/crc32.c
+	${zlib_SOURCE_DIR}/deflate.c
+	${zlib_SOURCE_DIR}/infback.c
+	${zlib_SOURCE_DIR}/inffast.c
+	${zlib_SOURCE_DIR}/inflate.c
+	${zlib_SOURCE_DIR}/inftrees.c
+	${zlib_SOURCE_DIR}/trees.c
+	${zlib_SOURCE_DIR}/zutil.c
+	${zlib_SOURCE_DIR}/compress.c
+	${zlib_SOURCE_DIR}/uncompr.c
+	${zlib_SOURCE_DIR}/gzclose.c
+	${zlib_SOURCE_DIR}/gzlib.c
+	${zlib_SOURCE_DIR}/gzread.c
+	${zlib_SOURCE_DIR}/gzwrite.c)
+
+add_library(ZLIB::ZLIB ALIAS zlibstatic)