Cmake refresh

Use target objects everywhere, and simplify handling of system vs
local dependencies.

3rdparty/CMakeLists.txt

@@ -2,6 +2,6 @@ if (NOT SYSTEM_EXPAT)
 	add_subdirectory(expat)
 endif()
 
-if (ENABLE_DNS AND NOT SYSTEM_UDNS)
+if (NOT SYSTEM_UDNS)
 	add_subdirectory(udns)
 endif()

3rdparty/expat/CMakeLists.txt

@@ -26,8 +26,24 @@ set(expat_sources
         sg_expat_external.h 
 	)
 
-foreach(s ${expat_sources})
-	set_property(GLOBAL
-		APPEND PROPERTY LOCAL_EXPAT_SOURCES 
-        "${CMAKE_CURRENT_SOURCE_DIR}/${s}")
-endforeach()
+add_library(FGExpat STATIC ${expat_sources})
+
+target_include_directories(FGExpat BEFORE PUBLIC
+    $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}>
+    $<INSTALL_INTERFACE:include>)
+
+# for the config file above
+target_include_directories(FGExpat PRIVATE ${PROJECT_BINARY_DIR}/3rdparty/expat)
+
+target_compile_definitions(FGExpat PUBLIC HAVE_SIMGEAR_EXPAT_CONFIG_H XML_STATIC)
+
+# look like Expat found by find()
+add_library(EXPAT::EXPAT ALIAS FGExpat)
+
+# in the non-shared case, we need to export these as well
+if (NOT SIMGEAR_SHARED)
+    install(TARGETS FGExpat
+        EXPORT SimGearTargets
+        LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
+        ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR})
+endif()

3rdparty/udns/CMakeLists.txt

@@ -13,7 +13,6 @@ CHECK_SYMBOL_EXISTS(AF_INET6 "netinet/in.h" HAVE_IPv6)
 check_include_file(windows.h  WINDOWS)
 
 CONFIGURE_FILE(${CMAKE_CURRENT_SOURCE_DIR}/config.h.in ${CMAKE_BINARY_DIR}/config.h)
-include_directories(${CMAKE_BINARY_DIR})
 
 set(HEADERS
 )
@@ -38,4 +37,21 @@ set(SOURCES
     udns_XtoX.c
 )
 
-simgear_component(udns 3rdparty/udns "${SOURCES}" "${HEADERS}")
+add_library(FGUdns STATIC ${SOURCES})
+
+target_include_directories(FGUdns BEFORE PUBLIC
+    $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}>
+    $<INSTALL_INTERFACE:include>)
+    
+target_include_directories(FGUdns PRIVATE ${CMAKE_BINARY_DIR})
+
+# match the name of imported UDns 
+add_librarY(Udns::Udns ALIAS FGUdns)
+
+# in the non-shared case, we need to export these as well
+if (NOT SIMGEAR_SHARED)
+    install(TARGETS FGUdns
+        EXPORT SimGearTargets
+        LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
+        ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR})
+endif()