libpam: update to 1.5.1

Fix installed paths. After e52d0487e88c3c8c57e1310d1a02b18eae0d142e
upstream, this bug was exposed.

Instead of working around it, fix the patch.

After this, everything consistently gets installed to ipkg-install/usr.

Minor Makefile reorganization.

Signed-off-by: Rosen Penev <rosenp@gmail.com>

libs/libpam/patches/0001-build-always-use-lib-instead-of-lib64.patch

@@ -1,36 +1,11 @@
-From 1948dd03d69c1a50e92d7e8868b7d6eabd4873c1 Mon Sep 17 00:00:00 2001
-From: Yousong Zhou <yszhou4tech@gmail.com>
-Date: Wed, 17 Jun 2015 16:11:31 +0800
-Subject: [PATCH 1/7] build: always use /lib instead of /lib64.
-
-* configure.ac: OpenWrt does not use /lib64.
-
-Signed-off-by: Yousong Zhou <yszhou4tech@gmail.com>
----
- configure.ac |   10 +---------
- 1 file changed, 1 insertion(+), 9 deletions(-)
-
-diff --git a/configure.ac b/configure.ac
-index fd0e310..306b6e2 100644
 --- a/configure.ac
 +++ b/configure.ac
-@@ -25,15 +25,7 @@ dnl If we use /usr as prefix, use /etc for config files
+@@ -25,7 +25,7 @@ dnl If we use /usr as prefix, use /etc f
          then
                  sysconfdir="/etc"
          fi
 -	if test ${libdir} = '${exec_prefix}/lib'
--	then
--		case "$host_cpu" in
--		    x86_64|ppc64|s390x|sparc64)
--			libdir="/lib64" ;;
--		    *)
--			libdir="/lib" ;;
--		esac
--	fi
-+	libdir="/lib"
- 	if test ${sbindir} = '${exec_prefix}/sbin'
-         then
-                 sbindir="/sbin"
--- 
-1.7.10.4
-
++	if false
+ 	then
+ 		case "$host_cpu" in
+ 		    x86_64|ppc64|s390x|sparc64)