spec: make it easier to autoreconf when building rpm

Over time, Fedora and RHEL RPMs have often backported upstream
patches that touched configure.ac and/or Makefile.am; this
necessitates rerunning the autotools for the patch to be effective.
Making this a one-liner spec tweak will make it easier for future
backports to pull patches without having to find all the places
to touch to properly use the autotools.  Meanwhile, there have been
historical instances where an update in the autotools caused FTBFS
situations, so this is not on by default.

* libvirt.spec.in (enable_autotools): New variable, default off.
(BuildRequires): Conditionally add autotools.
(%build): Conditionally use them before configure.
* mingw32-libvirt.spec.in: Likewise.

libvirt.spec.in

@@ -8,6 +8,11 @@
   sed -ne 's/^\.fc\?\([0-9]\+\).*/%%define fedora \1/p')}
 %endif
 
+# Default to skipping autoreconf.  Distros can change just this one line
+# (or provide a command-line override) if they backport any patches that
+# touch configure.ac or Makefile.am.
+%{!?enable_autotools:%define enable_autotools 0}
+
 # A client only build will create a libvirt.so only containing
 # the generic RPC driver, and test driver and no libvirtd
 # Default to a full server + client build
@@ -349,6 +354,12 @@ Requires(postun): systemd-units
 %endif
 
 # All build-time requirements
+%if 0%{?enable_autotools}
+BuildRequires: autoconf
+BuildRequires: automake
+BuildRequires: gettext-devel
+BuildRequires: libtool
+%endif
 BuildRequires: python-devel
 %if %{with_systemd}
 BuildRequires: systemd-units
@@ -729,6 +740,9 @@ of recent versions of Linux (and other OSes).
 %define init_scripts --with-init_script=redhat
 %endif
 
+%if 0%{?enable_autotools}
+autoreconf -if
+%endif
 %configure %{?_without_xen} \
            %{?_without_qemu} \
            %{?_without_openvz} \

mingw32-libvirt.spec.in

@@ -5,6 +5,11 @@
 %define __find_provides %{_mingw32_findprovides}
 %define __debug_install_post %{_mingw32_debug_install_post}
 
+# Default to skipping autoreconf.  Distros can change just this one line
+# (or provide a command-line override) if they backport any patches that
+# touch configure.ac or Makefile.am.
+%{!?enable_autotools:%define enable_autotools 0}
+
 # The mingw build is client only.  Set up defaults for hypervisor drivers
 # that talk via a native remote protocol, and for which prereq mingw
 # libraries exist.
@@ -44,6 +49,12 @@ BuildRequires:  mingw32-portablexdr
 BuildRequires:  pkgconfig
 # Need native version for msgfmt
 BuildRequires:  gettext
+%if 0%{?enable_autotools}
+BuildRequires: autoconf
+BuildRequires: automake
+BuildRequires: gettext-devel
+BuildRequires: libtool
+%endif
 
 %if %{with_phyp}
 BuildRequires: mingw32-libssh2
@@ -81,6 +92,9 @@ MinGW Windows libvirt virtualization library.
 %define _without_xenapi --without-xenapi
 %endif
 
+%if 0%{?enable_autotools}
+autoreconf -if
+%endif
 # XXX enable SASL in future
 %{_mingw32_configure} \
   --without-xen \