package/libselinux: fix build with musl

musl does not define glibcisms, so we are missing some macros.

Define what we need in case the macro is missing. We're using a dumb
implementation, which is rather slow, to avoid copying from glibc, to
avoid propagating the LGPL to libselinux, which is Public Domain.

Fixes a bunch of autobuild failures:
    http://autobuild.buildroot.org/results/d4d/d4d209719d1ce5219f84719ad72fcb6a0c684007/
    http://autobuild.buildroot.org/results/1a6/1a65cc3d2c23a3c17c605788be62dbd18cbdaf76/
    http://autobuild.buildroot.org/results/0d0/0d0e4713833182d0f634b9b39b2c56f2bc0adcac/
    ...

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Clayton Shotwell <clshotwe@rockwellcollins.com>
Reviewed-by: Clayton Shotwell <clayton.shotwell@rockwellcollins.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/libselinux/0002-fix-musl-build.patch

@@ -0,0 +1,30 @@
+fix undefined macros in musl
+
+musl does not define glibc-specific macros, so use a simple version of
+the macro when it is not defined.
+
+This is very inefficient, however, but copying the code from glibc is
+not really possible because it is LGPL while libselinux in Public
+Domain, and we want to avoid license propagation, so this macro is
+completely written from scratch, and non-optimal.
+
+Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
+
+diff -durN libselinux-2.1.13.orig/src/booleans.c libselinux-2.1.13/src/booleans.c
+--- libselinux-2.1.13.orig/src/booleans.c	2013-02-06 02:43:22.000000000 +0100
++++ libselinux-2.1.13/src/booleans.c	2015-07-26 20:40:41.311801914 +0200
+@@ -62,6 +62,14 @@
+ 		goto bad;
+ 	}
+ 
++/* Simple (but inefficient) version of _D_ALLOC_NAMLEN when
++ * building with a C library that misses it (e.g. musl).
++ * Note: glibc does a strlen on (d)->d_name, so assume it is safe.
++ */
++#ifndef _D_ALLOC_NAMLEN
++#define _D_ALLOC_NAMLEN(d) (strlen((d)->d_name)+1)
++#endif
++
+ 	for (i = 0; i < *len; i++) {
+ 		n[i] = (char *)malloc(_D_ALLOC_NAMLEN(namelist[i]));
+ 		if (!n[i]) {