[GlobalISel][X86] extend G_ZEXT support.

Summary:
Mark G_ZEXT/G_SEXT i1 to i8/i16,  i8 to i16 as legal.
Support G_ZEXT i1 to i8/i16 instruction selection ( C++ code).
This patch requred to support G_LOAD/G_STORE i1.

Reviewers: zvi, guyblank

Reviewed By: guyblank

Subscribers: rovka, llvm-commits, kristof.beyls

Differential Revision: https://reviews.llvm.org/D35177

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@307526 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed