Don't remove generated files on clean

When generated files are removed on clean, the build will
fail because log4cxx.h is not found, and cmake must be run
again.  The files still get regenrated anyway.
diff --git a/src/main/include/CMakeLists.txt b/src/main/include/CMakeLists.txt
index a8b0f40..97f286d 100644
--- a/src/main/include/CMakeLists.txt
+++ b/src/main/include/CMakeLists.txt
@@ -10,9 +10,6 @@
   DEPENDS
     ${CMAKE_CURRENT_SOURCE_DIR}/log4cxx/log4cxx.hw
     ${CMAKE_CURRENT_SOURCE_DIR}/log4cxx/private/log4cxx_private.hw
-  BYPRODUCTS
-    ${CMAKE_CURRENT_BINARY_DIR}/log4cxx/log4cxx.h
-    ${CMAKE_CURRENT_BINARY_DIR}/log4cxx/private/log4cxx_private.h
 )
 configure_file(${CMAKE_CURRENT_SOURCE_DIR}/log4cxx/version_info.h.in
                ${CMAKE_CURRENT_BINARY_DIR}/log4cxx/version_info.h
@@ -112,8 +109,5 @@
   DEPENDS
     ${CMAKE_CURRENT_SOURCE_DIR}/log4cxx/log4cxx.h.in
     ${CMAKE_CURRENT_SOURCE_DIR}/log4cxx/private/log4cxx_private.h.in
-  BYPRODUCTS
-    ${CMAKE_CURRENT_BINARY_DIR}/log4cxx/log4cxx.h
-    ${CMAKE_CURRENT_BINARY_DIR}/log4cxx/private/log4cxx_private.h
 )
 endif()