cmake: fix out-of-source build

Generate config_types in the build directory instead of
the source directory.

Signed-off-by: Ralph Giles <giles@thaumas.net>
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 78b6604..c21e5ce 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -43,7 +43,7 @@
     set(includedir ${CMAKE_INSTALL_FULL_INCLUDEDIR})
     set(VERSION ${PROJECT_VERSION})
     string(REPLACE ".in" "" pkg_config_file ${pkg_config_file_in})
-    configure_file(${pkg_config_file_in} ${CMAKE_CURRENT_SOURCE_DIR}/${pkg_config_file} @ONLY)
+    configure_file(${pkg_config_file_in} ${CMAKE_CURRENT_BINARY_DIR}/${pkg_config_file} @ONLY)
 endfunction()
 
 message(STATUS "Configuring ${PROJECT_NAME} ${PROJECT_VERSION}")
@@ -59,7 +59,7 @@
 set(USIZE32 uint32_t)
 set(SIZE64 int64_t)
 
-configure_file(include/ogg/config_types.h.in ${CMAKE_CURRENT_SOURCE_DIR}/include/ogg/config_types.h @ONLY)
+configure_file(include/ogg/config_types.h.in ${CMAKE_CURRENT_BINARY_DIR}/include/ogg/config_types.h @ONLY)
 
 set(OGG_HEADERS
     include/ogg/config_types.h