[Bug target/89456] New: target attribute doesn't work well with -march=native

[hjl.tools at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89456

            Bug ID: 89456
           Summary: target attribute doesn't work well with -march=native
           Product: gcc
           Version: 9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hjl.tools at gmail dot com
  Target Milestone: ---
            Target: i386,x86-64

-march=native is expanded to -march=xxx -myyy -mno-zzz.  Whe compiling

int __attribute__ ((target("arch=broadwell"))) foo () {
  return 13; 
}

arch=broadwell won't set x_ix86_isa_flags since x_ix86_isa_flags_explicit
has been set via command line.  As the result, all_ix86_isa_flags checks
in get_builtin_code_for_version will be wrong.