When moving zext/sext to be folded with a load, ignore the issue of whether

When moving zext/sext to be folded with a load, ignore the issue of whether
truncates are free only in the case where the extended type is legal but the
load type is not.  If both types are illegal, such as when they are too big,
the load may not be legalized into an extended load.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@114568 91177308-0d34-0410-b5e6-96231b3b80d8