Make various error-related globals thread-local

This changes bfd_error et al to be thread-local.

	* Makefile.in: Regenerate.
	* aclocal.m4: Include ax_tls.m4.
	* ax_tls.m4: New file.
	* bfd.c: (bfd_error, input_error, input_bfd, _bfd_error_buf):
	Now thread-local.
	(bfd_asprintf): Update docs.
	* config.in, configure: Regenerate.
	* configure.ac: Call AX_TLS.
	* po/bfd.pot: Regenerate.
8 files changed