[Bug pch/86007] New: precompiled header on bdver2 with -march=native triggers a "created and used with differing settings of '-mlwp'" warning, intermittently

["stefantalpalaru at yahoo dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86007

            Bug ID: 86007
           Summary: precompiled header on bdver2 with -march=native
                    triggers a "created and used with differing settings
                    of '-mlwp'" warning, intermittently
           Product: gcc
           Version: 8.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: pch
          Assignee: unassigned at gcc dot gnu.org
          Reporter: stefantalpalaru at yahoo dot com
  Target Milestone: ---

I came upon this bug in a more complex case, when compiling Natron on Gentoo
~amd64 when the PCH compilation warning turned into a "one or more PCH files
were found, but they were invalid" error later on:
https://github.com/4nykey/4nykey/issues/20

I managed to come up with a simple test case replicating only the warning,
intermittently:
https://gist.github.com/stefantalpalaru/3e984cf56c2eea462ae761143e0d0dfd

I hope it's enough to figure out why -march=native can fail to detect LWP when
creating the precompiled header on my FX-8320E.

It might be related to this builtin arch detection bug that is also manifested
on my CPU: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85591