cppfiles.c (stack_include_file): Push zero-length buffers in case of failure.
* cppfiles.c (stack_include_file): Push zero-length buffers
in case of failure. Return void, as we don't fail any more.
(read_include_file): Check for files we shouldn't re-read.
Don't return an error code; errors are implied by marking the
file NEVER_REREAD.
(_cpp_execute_include): Move the recursion and in-macro checks
here. Update for stack_include_file not failing.
* cpplib.c (cpp_push_buffer): Always succeed, since
_cpp_execute_include performs the recursion check. Tidy up.
* cpplib.h (cpp_push_buffer): Update prototype.