Promote generated headers to regular headers. This enables direct
editing of corresponding files and running automatic source code
formatting and static analysis tools, such as clang-format and
clang-tidy on the whole project which previously was not
straightforward.
It looks like commit 3c49b93 modified the auto-generated file src/config.h.in
to add a definition of macro GOOGLE_GLOG_DLL_DECL. One of the autotools
reverts this change upon running "make", causing the build to fail when a
source file includes demangle.h.
To fix the problem, revert the change to src/config.h.in and include
glog/logging.h from demangle.h which provides a definition of that macro.
