Handle static CURL

(Especially) on Windows we need to define `CURL_STATICLIB` when linking
to the static curl library or we get errors such as:
> unresolved external symbol __imp__curl_free

Check if the CURL target from the CMake config file (of CURL) was used
and trust them to set that define.
Otherwise apply a heuristic to detect whether static CURL was found and
set the define in that case

src/CMakeLists.txt

@@ -14,8 +14,20 @@ endif()
 rttr_set_output_dir(RUNTIME ${RTTR_EXTRA_BINDIR})
 
 add_executable(s25update ${_sources})
-target_include_directories(s25update SYSTEM PRIVATE ${CURL_INCLUDE_DIRS})
-target_link_libraries(s25update PRIVATE s25util::common ${CURL_LIBRARIES} BZip2::BZip2 Boost::filesystem Boost::nowide Boost::disable_autolinking)
+
+if (TARGET CURL::libcurl AND CURL_CONFIG)
+	target_link_libraries(s25update PRIVATE CURL::libcurl)
+else()
+	target_include_directories(s25update SYSTEM PRIVATE ${CURL_INCLUDE_DIRS})
+	target_link_libraries(s25update PRIVATE ${CURL_LIBRARIES})
+	# Heuristic if CURL is a static library and we need to add the define
+	if(CURL_LIBRARIES MATCHES "\.a$" OR CURL_LIBRARIES MATCHES "curl_a" OR (WIN32 AND NOT CURL_LIBRARIES MATCHES "_imp\.lib"))
+		target_compile_definitions(s25update PRIVATE "CURL_STATICLIB")
+	endif()
+endif()
+
+target_include_directories(s25update SYSTEM PRIVATE)
+target_link_libraries(s25update PRIVATE s25util::common BZip2::BZip2 Boost::filesystem Boost::nowide Boost::disable_autolinking)
 target_compile_features(s25update PRIVATE cxx_std_17)
 if(NOT PLATFORM_NAME OR NOT PLATFORM_ARCH)
 	message(FATAL_ERROR "PLATFORM_NAME or PLATFORM_ARCH not set")