[Bug target/83546] New: -march=silvermont doesn't enable rdrnd by default despite what docs say

[craig.topper at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83546

            Bug ID: 83546
           Summary: -march=silvermont doesn't enable rdrnd by default
                    despite what docs say
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: craig.topper at gmail dot com
  Target Milestone: ---

The documentation https://gcc.gnu.org/onlinedocs/gcc/x86-Options.html says
'silvermont' enables rdrnd, but that doesn't appear to happen. 

I think it may have worked in r205275 when 'slm' listed all of its features
separately.

But I think it was then broken in r206178 when PTA_SILVERMONT was introduced
and defined like this

  #define PTA_SILVERMONT \
    (PTA_WESTMERE | PTA_MOVBE)


PTA_WESTMERE doesn't and shouldn't include RDRND.