Wrap <pwd.h> so that calls go direct and the symbols are all weak.

Hide bcrypt_autorounds(), prefixing with an underbar for static builds.

src/lib/libc/crypt/bcrypt.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: bcrypt.c,v 1.54 2015/09/13 12:42:39 millert Exp $	*/
+/*	$OpenBSD: bcrypt.c,v 1.55 2015/09/13 15:33:48 guenther Exp $	*/
 
 /*
  * Copyright (c) 2014 Ted Unangst <tedu@openbsd.org>
@@ -215,6 +215,7 @@ bcrypt_newhash(const char *pass, int log_rounds, char *hash, size_t hashlen)
 	explicit_bzero(salt, sizeof(salt));
 	return 0;
 }
+DEF_WEAK(bcrypt_newhash);
 
 int
 bcrypt_checkpass(const char *pass, const char *goodhash)
@@ -232,13 +233,14 @@ bcrypt_checkpass(const char *pass, const char *goodhash)
 	explicit_bzero(hash, sizeof(hash));
 	return 0;
 }
+DEF_WEAK(bcrypt_checkpass);
 
 /*
  * Measure this system's performance by measuring the time for 8 rounds.
  * We are aiming for something that takes around 0.1s, but not too much over.
  */
 int
-bcrypt_autorounds(void)
+_bcrypt_autorounds(void)
 {
 	struct timespec before, after;
 	int r = 8;
@@ -391,3 +393,4 @@ bcrypt(const char *pass, const char *salt)
 
 	return gencrypted;
 }
+DEF_WEAK(bcrypt);

src/lib/libc/crypt/cryptutil.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: cryptutil.c,v 1.11 2015/09/12 14:56:50 guenther Exp $ */
+/* $OpenBSD: cryptutil.c,v 1.12 2015/09/13 15:33:48 guenther Exp $ */
 /*
  * Copyright (c) 2014 Ted Unangst <tedu@openbsd.org>
  *
@@ -21,8 +21,6 @@
 #include <login_cap.h>
 #include <errno.h>
 
-int bcrypt_autorounds(void);
-
 int
 crypt_checkpass(const char *pass, const char *goodhash)
 {
@@ -70,12 +68,12 @@ crypt_newhash(const char *pass, const char *pref, char *hash, size_t hashlen)
 		const char *choice = choices[i];
 		size_t len = strlen(choice);
 		if (strcmp(pref, choice) == 0) {
-			rounds = bcrypt_autorounds();
+			rounds = _bcrypt_autorounds();
 			break;
 		} else if (strncmp(pref, choice, len) == 0 &&
 		    pref[len] == ',') {
 			if (strcmp(pref + len + 1, "a") == 0) {
-				rounds = bcrypt_autorounds();
+				rounds = _bcrypt_autorounds();
 			} else {
 				rounds = strtonum(pref + len + 1, 4, 31, &errstr);
 				if (errstr) {