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.

libctf/ctf-sha1.c

@@ -0,0 +1,50 @@
+/* SHA-1 thunks.
+   Copyright (C) 2019 Free Software Foundation, Inc.
+
+   This file is part of libctf.
+
+   libctf is free software; you can redistribute it and/or modify it under
+   the terms of the GNU General Public License as published by the Free
+   Software Foundation; either version 3, or (at your option) any later
+   version.
+
+   This program is distributed in the hope that it will be useful, but
+   WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+   See the GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; see the file COPYING.  If not see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <ctf-impl.h>
+#include <ctf-sha1.h>
+
+static const char hex[] = "0123456789abcdef";
+
+char *
+ctf_sha1_fini (ctf_sha1_t *sha1, char *buf)
+{
+  size_t i;
+
+  /* Alignment suitable for a uint32_t. */
+  union
+  {
+    uint32_t align;
+    unsigned char digest[((CTF_SHA1_SIZE - 1) / 2) + 1];
+  } align;
+
+  sha1_finish_ctx (sha1, align.digest);
+
+  if (!buf)
+    return NULL;
+
+  buf[CTF_SHA1_SIZE - 1] = '\0';
+
+  for (i = 0; i < (CTF_SHA1_SIZE - 1) / 2; i++)
+    {
+      buf[2 * i] = hex[align.digest[i] >> 4];
+      buf[2 * i + 1] = hex[align.digest[i] & 0xf];
+    }
+  return buf;
+}