Msys2 Makefile: Handle icu version with a single variable
Rework Msys2 Makefile so that icu version is given in one place only (as a value for a variable), and not separately in each icu file name.
Rework Msys2 Makefile so that icu version is given in one place only (as a value for a variable), and not separately in each icu file name.