spec: Make the build reproducible

If the spec file applies a patch which touches any file in the API XMLs
dependency tree, we need to regenerate the XMLs and consequently
recreate hvsupport.html. The file will contain a time stamp in a comment
which means it will be different every time the package is built. The
commit a54c9622 which added the time stamp also added support for
SOURCE_DATE_EPOCH environment variable. Let's set it to the time stamp
of the spec file itself to make the build reproducible.
Signed-off-by: NJiri Denemark <jdenemar@redhat.com>
Reviewed-by: NPino Toscano <ptoscano@redhat.com>

libvirt.spec.in

@@ -1300,6 +1300,8 @@ exit 1
 
 # place macros above and build commands below this comment
 
+export SOURCE_DATE_EPOCH=$(stat --printf='%Y' %{_specdir}/%{name}.spec)
+
 %if 0%{?enable_autotools}
  autoreconf -if
 %endif
@@ -1372,6 +1374,8 @@ gzip -9 ChangeLog
 %install
 rm -fr %{buildroot}
 
+export SOURCE_DATE_EPOCH=$(stat --printf='%Y' %{_specdir}/%{name}.spec)
+
 # Avoid using makeinstall macro as it changes prefixes rather than setting
 # DESTDIR. Newer make_install macro would be better but it's not available
 # on RHEL 5, thus we need to expand it here.