libchdr: add build option for using system library

The added build option USE_HOST_LIBCHDR allows to build with libchdr provided by
the system. The option is disabled by default.

CMakeLists.txt

@@ -58,6 +58,7 @@ option(USE_GLES2 "Use GLES2 API" OFF)
 option(USE_HOST_GLSLANG "Use host glslang" OFF)
 option(USE_HOST_LIBZIP "Use host libzip" ON)
 option(USE_HOST_SDL "Use host SDL library" ${USE_HOST_SDL_DEFAULT})
+option(USE_HOST_LIBCHDR "Use host libchdr" OFF)
 option(USE_OPENMP "Use OpenMP if available" ON)
 option(USE_VULKAN "Build with Vulkan support" ON)
 option(USE_DX9 "Build with Direct3D 9 support" ON)
@@ -481,9 +482,15 @@ if(NOT LIBRETRO)
 	endif()
 endif()
 
-add_subdirectory(core/deps/libchdr EXCLUDE_FROM_ALL)
-target_link_libraries(${PROJECT_NAME} PRIVATE chdr-static)
-target_include_directories(${PROJECT_NAME} PRIVATE core/deps/libchdr/include)
+find_package(PkgConfig)
+if(PKG_CONFIG_FOUND AND USE_HOST_LIBCHDR AND NOT LIBRETRO)
+	pkg_check_modules(LIBCHDR IMPORTED_TARGET libchdr)
+	target_link_libraries(${PROJECT_NAME} PRIVATE PkgConfig::LIBCHDR)
+else()
+	add_subdirectory(core/deps/libchdr EXCLUDE_FROM_ALL)
+	target_link_libraries(${PROJECT_NAME} PRIVATE chdr-static)
+	target_include_directories(${PROJECT_NAME} PRIVATE core/deps/libchdr/include)
+endif()
 
 if(NOT WITH_SYSTEM_ZLIB)
 	set(ZLIB_RELATIVE_PATH "core/deps/libchdr/deps/zlib-1.3.1")
@@ -497,7 +504,6 @@ if(NOT WITH_SYSTEM_ZLIB)
 	get_target_property(ZLIB_LIBRARY_DEBUG zlibstatic LOCATION_Debug)
 endif()
 
-find_package(PkgConfig)
 if(PKG_CONFIG_FOUND AND NOT ANDROID AND NOT APPLE AND NOT LIBRETRO)
 	if(USE_LIBAO)
 		pkg_check_modules(AO IMPORTED_TARGET ao)