Export flac properly when use with add_subdirectory (#285)

This allows for flac to be used in a larger CMake project
with add_subdirectory. It also allows for Ogg to be
build elsewhere in the larger project.

CMakeLists.txt

@@ -42,7 +42,11 @@ if(WITH_OGG)
             set_target_properties(test_bitwise test_framing PROPERTIES FOLDER Tests)
         endif()
     else()
-        find_package(Ogg REQUIRED)
+        if(NOT TARGET Ogg::ogg)
+            find_package(Ogg REQUIRED)
+        else()
+            set(OGG_FOUND 1 CACHE INTERNAL "ogg has already been built")
+        endif()
         set(OGG_PACKAGE "ogg")
     endif()
 endif()
@@ -228,12 +232,18 @@ if(INSTALL_CMAKE_CONFIG_MODULE)
         EXPORT targets
         DESTINATION "${CMAKE_INSTALL_DATADIR}/${PROJECT_NAME}/cmake"
         NAMESPACE FLAC::)
+    export(EXPORT targets NAMESPACE FLAC:: FILE FLACTargets.cmake)
 
     configure_package_config_file(
-        flac-config.cmake.in flac-config.cmake
+        ${PROJECT_SOURCE_DIR}/flac-config.cmake.in ${CMAKE_CURRENT_BINARY_DIR}/flac-config.cmake
         INSTALL_DESTINATION "${CMAKE_INSTALL_DATADIR}/${PROJECT_NAME}/cmake")
     write_basic_package_version_file(
-        flac-config-version.cmake COMPATIBILITY AnyNewerVersion)
+        ${CMAKE_CURRENT_BINARY_DIR}/flac-config-version.cmake COMPATIBILITY AnyNewerVersion)
+
+    install(
+        FILES ${CMAKE_CURRENT_BINARY_DIR}/flac-config.cmake ${CMAKE_CURRENT_BINARY_DIR}/flac-config-version.cmake
+        DESTINATION "${CMAKE_INSTALL_DATADIR}/${PROJECT_NAME}/cmake"
+    )
 
     install(
         FILES

flac-config.cmake.in

@@ -1,7 +1,9 @@
 @PACKAGE_INIT@
 
 include(CMakeFindDependencyMacro)
-find_dependency(Ogg)
+if(NOT TARGET Ogg::ogg)
+    find_dependency(Ogg)
+endif()
 
 include("${CMAKE_CURRENT_LIST_DIR}/targets.cmake")