v3.28-zos-beta.4: avoid unnecessary XL constraint for compiler version > v2r2

from the IO for asm:
Note: The use of the XL prefix for these constraints is optional.
This means that the parameters defined for the XL constraint can be
used without the "XL:" prefix (i.e NR:r8 is the same as XL:NR:r8)

v3.28-zos-beta.3

first tech preview