libctf: add SHA-1 support for libctf

libctf: add SHA-1 support for libctf

This very thin abstraction layer provides SHA-1ing facilities to all of
libctf, almost all inlined wrappers around the libiberty functionality
other than ctf_sha1_fini.

The deduplicator will use this to recursively hash types to prove their
identity.

libctf/
	* ctf-sha1.h: New, inline wrappers around sha1_init_ctx and
	sha1_process_bytes.
	* ctf-impl.h: Include it.
	(ctf_sha1_init): New.
	(ctf_sha1_add): Likewise.
	(ctf_sha1_fini): Likewise.
	* ctf-sha1.c: New, non-inline wrapper around sha1_finish_ctx
	producing strings.
	* Makefile.am: Add file.
	* Makefile.in: Regenerate.