[X86] Don't transform X << 1 to X + X during type legalization

While legalizing a 64-bit shift left by 1, the following occurs:

We split the shift operand in half: a high half and a low half.
We then create an ADDC with the low half and a ADDE with the high half +
the carry bit from the ADDC.

This is problematic if X is any_ext'd because the high half computation
is now undef + undef + carry bit and there is no way to ensure that the
two undef values had the same bitwise representation.  This results in
the lowest bit in the high half turning into garbage.

Instead, do not try to turn shifts into arithmetic during type
legalization.

This fixes PR26350.

llvm-svn: 259065