Move platform dependent errno aliases

EBADE, EBADR, and ENOANO do not exist on FreeBSD

The libspl errno.h is similarly platform dependent.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Matt Macy <mmacy@FreeBSD.org>
Closes #9498

lib/libspl/include/os/linux/sys/Makefile.am

@@ -1,6 +1,7 @@
 libspldir = $(includedir)/libspl/sys
 libspl_HEADERS = \
 	$(top_srcdir)/lib/libspl/include/os/linux/sys/byteorder.h \
+	$(top_srcdir)/lib/libspl/include/os/linux/sys/errno.h \
 	$(top_srcdir)/lib/libspl/include/os/linux/sys/file.h \
 	$(top_srcdir)/lib/libspl/include/os/linux/sys/mnttab.h \
 	$(top_srcdir)/lib/libspl/include/os/linux/sys/mount.h \

lib/libspl/include/os/linux/sys/errno.h

@@ -0,0 +1,46 @@
+/*
+ * CDDL HEADER START
+ *
+ * The contents of this file are subject to the terms of the
+ * Common Development and Distribution License, Version 1.0 only
+ * (the "License").  You may not use this file except in compliance
+ * with the License.
+ *
+ * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
+ * or http://www.opensolaris.org/os/licensing.
+ * See the License for the specific language governing permissions
+ * and limitations under the License.
+ *
+ * When distributing Covered Code, include this CDDL HEADER in each
+ * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
+ * If applicable, add the following below this CDDL HEADER, with the
+ * fields enclosed by brackets "[]" replaced with your own identifying
+ * information: Portions Copyright [yyyy] [name of copyright owner]
+ *
+ * CDDL HEADER END
+ */
+/*
+ * Copyright 2017 Zettabyte Software, LLC.  All rights reserved.
+ * Use is subject to license terms.
+ */
+
+/*
+ * Compiling against musl correctly points out that including sys/errno.h is
+ * disallowed by the Single UNIX Specification when building in userspace, so
+ * we implement a dummy header to redirect the include to the proper header.
+ */
+#ifndef _LIBSPL_SYS_ERRNO_H
+#define	_LIBSPL_SYS_ERRNO_H
+
+#include <errno.h>
+/*
+ * We'll take the unused errnos, 'EBADE' and 'EBADR' (from the Convergent
+ * graveyard) to indicate checksum errors and fragmentation.
+ */
+#define	ECKSUM	EBADE
+#define	EFRAGS	EBADR
+
+/* Similar for ENOACTIVE */
+#define	ENOTACTIVE	ENOANO
+
+#endif /* _LIBSPL_SYS_ERRNO_H */