[LVU] set ppc64 blockage's length to zero

[LVU] set ppc64 blockage's length to zero

LVU requires the zero-length (pseudo) insns's length to reflect
reality.  If they don't, it may assume there's a PC change where there
isn't any, and then a view-aware assembler will detect the problem and
complain about out-of-sync views.

ppc blockage pseudo-insns did not have the length attribute explicitly
set in them, so they inherited the attribute's default value, and that
was nonzero.

for  gcc/ChangeLog

	* config/rs6000/rs6000.md (blockage): Set length to zero.

From-SVN: r257520