Update shift left that might cause ub
Update shift left that might cause ub

A few shift lefts cause ub because of `(1 << n)` where `n` is 31. 
The constant 1 is signed causing ub. Initially my fix was to do `(1U << n)` however, I have seen the pattern `((U32)1 << n)` elsewhere in the file so decided to follow this.

Caught by ubsan racketcs.
mflatt/ChezScheme,mflatt/ChezScheme,mflatt/ChezScheme