MFC r259498:

Pull in r197399 from upstream clang trunk:

  Add bit_FXSAVE as an alias for bit_FXSR, for gcc compat.
Honor WITHOUT_SYSINSTALL=1.

This is a direct commit to stable/9.

PR:		176263
Submitted by:	Sayetsky Anton  (vsjcfm gmail com)
Sponsored by:	The FreeBSD Foundation
[automated] Merge in upstream-github/stable/9