FIX #2047: Windows (and older Unixes): align info tables to 4 bytes, not 2

FIX #2047: Windows (and older Unixes): align info tables to 4 bytes, not 2
Perhaps in the past '.align 2' meant align to 4 bytes, but nowadays it
means align to 2 bytes.  The compacting collector requires info tables
to be aligned to 4 bytes, because it stores tag bits in the low 2
bits.

This only affects -fvia-C - the native code generator was already
emitting the correct alignment.  The incorrect alignment might well
have been adversely affecting performance with -fvia-C on Windows.