LIBVIRT_ARG_WITH_ALT is more generic than LIBVIRT_ARG_WITH, which
is tailored at switching features on and off.

Rename the macros according to their intended purpose, and add
some documentation to help developers pick between the two.

Usage of AC_REQUIRE will mess with order how LIBVIRT_CHECK_* macros
are composed into configure.ac.  This ensures that the output of
configure --help is properly ordered and grouped into sections.
Signed-off-by: NPavel Hrdina <phrdina@redhat.com>

Following patch will update LIBVIRT_CHECK_(LIB|LIB_ALT|PKG) macros in
a way that you will be able to call a another macro as a fallback if
the first one fails.  To allow that, we need to move the
LIBVIRT_ARG_WITH out of those macro to not have two or more same lines
in output of "configure --help".
Signed-off-by: NPavel Hrdina <phrdina@redhat.com>

Signed-off-by: NPavel Hrdina <phrdina@redhat.com>

Yet again, selinux has been adding const-correctness; this change
is ABI-compatible, but breaks API, which affects us when we try to
override things in our testsuite:

../../tests/securityselinuxhelper.c:307:24: error: conflicting types for 'selabel_open'
 struct selabel_handle *selabel_open(unsigned int backend,
                        ^~~~~~~~~~~~
In file included from ../../tests/securityselinuxhelper.c:32:0:
/usr/include/selinux/label.h:73:24: note: previous declaration of 'selabel_open' was here

The problem is a new 'const' prior to the second parameter.

Fix it the same way we did in commit 292d3f2d: check for the new
const at configure time.
Signed-off-by: NEric Blake <eblake@redhat.com>

Use correct variable name.

* m4/virt-selinux.m4: Fix one last variable name.

Commit 292d3f2d fixed the build with libselinux 2.3, but missed
some suggestions by eblake

https://www.redhat.com/archives/libvir-list/2014-May/msg00977.html

This patch changes the macro introduced in 292d3f2d to either be
empty in the case of newer libselinux, or contain 'const' in the
case of older libselinux.  The macro is then used directly in
tests/securityselinuxhelper.c.

Several function signatures changed in libselinux 2.3, now taking
a 'const char *' instead of 'security_context_t'.  The latter is
defined in selinux/selinux.h as

  typedef char *security_context_t;
Signed-off-by: NEric Blake <eblake@redhat.com>

Autoconf states that AC_HELP_STRING is obsolete, and that new
programs should use AS_HELP_STRING.  We also had instances of
not properly quoting the macro usage, and not relying on autoconf's
word-wrapping abilities to avoid long lines.  I validated that this
commit has no impact to the generated configure file.

* configure.ac (AC_ARG_WITH, AC_ARG_ENABLE): Autoconf recommends
the use of AS_HELP_STRING.  Also, use proper quoting and wrap long
lines.
* m4/virt-apparmor.m4 (LIBVIRT_CHECK_APPARMOR): Likewise.
* m4/virt-selinux.m4 (LIBVIRT_CHECK_SELINUX): Likewise.
Signed-off-by: NEric Blake <eblake@redhat.com>

Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>