[SPARC] Prevent -mfix-ut699 from generating b2bst errata sequences

[SPARC] Prevent -mfix-ut699 from generating b2bst errata sequences

The sequence
  st
  fdivd / fsqrtd
  std
was generated in some cases with -mfix-ut699 when there was
a st before the div/sqrt. This sequence could trigger the b2bst errata.

Now the following safe sequence is generated instead:
  st
  nop
  fdivd / fsqrtd
  std

2017-11-29  Martin Aberg  <maberg@gaisler.com>

gcc/
	* config/sparc/sparc.md (divdf3_fix): Add NOP and adjust length
        to prevent b2bst errata sequence.
        (sqrtdf2_fix): Likewise.

From-SVN: r255238