[X86] Fix some vector cmp builtins - TRUE/FALSE predicates

This patch removes on optimization used with the TRUE/FALSE
predicates, as was suggested in https://reviews.llvm.org/D45616
for r335339.
The optimization was buggy, since r335339 used it also
for *_mask builtins, without actually applying the mask -- the
mask argument was just ignored.

Reviewers: craig.topper, uriel.k, RKSimon, andrew.w.kaylor, spatel, scanon, efriedma

Reviewed By: spatel

Differential Revision: https://reviews.llvm.org/D48715

llvm-svn: 336355