Revert "i965/fs: Remove force_writemask_all assertion for execsize < 8."
Revert "i965/fs: Remove force_writemask_all assertion for execsize < 8."

This reverts commit 0d8f27eab7b7e8b7a16e76aabd3f6a0ab4880497.

"This doesn't seem to be necessary." <- I was wrong!

Tested-by: Markus Wick <300a2d193222dd0c23d880e16d727d352b404a01@selfnet.de>
Reviewed-by: Francisco Jerez <5906ff32bdd9fd8db196f6ba5ad3afd6f9257ea5@riseup.net>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler