[X86] Fast-ISel was incorrectly always killing the source of a truncate.

[X86] Fast-ISel was incorrectly always killing the source of a truncate.

A trunc from i32 to i1 on x86_64 generates an instruction such as

%vreg19<def> = COPY %vreg9:sub_8bit<kill>; GR8:%vreg19 GR32:%vreg9

However, the copy here should only have the kill flag on the 32-bit path, not the 64-bit one.
Otherwise, we are killing the source of the truncate which could be used later in the program.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@236890 91177308-0d34-0410-b5e6-96231b3b80d8