The sign-file.c program actually uses CMS rather than PKCS#7 to sign a file
since that allows the target X.509 certificate to be specified by
subjectKeyId rather than by issuer + serialNumber.

However, older versions of the OpenSSL crypto library (such as may be found
in CentOS 5.11) don't support CMS.  Assume everything prior to
OpenSSL-1.0.0 doesn't support CMS and switch to using PKCS#7 in that case.

Further, the pre-1.0.0 OpenSSL only supports PKCS#7 signing with SHA1, so
give an error from the sign-file script if the caller requests anything
other than SHA1.

The compiler gives the following error with an OpenSSL crypto library
that's too old:

  HOSTCC  scripts/sign-file
scripts/sign-file.c:23:25: fatal error: openssl/cms.h: No such file or directory
 #include <openssl/cms.h>

Reported-by: Vinson Lee <vlee@twopensource.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: David Woodhouse <David.Woodhouse@intel.com>