Add support for detecting RDSEED and ADX instructions.
Use RDSEED instead of RTM to ascertain that the CPU is
Broadwell or later in recog_intel.c. This fixes
detection discrepancies on Linux, where RTM is not
made available (I guess there's no kernel support for it).
The two new flags are also now detected in the Broadwell
and Skylake tests. Update them as well.