markers: ensure assembly is portable by using .hword instead of .word

http://www.chemie.fu-berlin.de/chemnet/use/info/gas/gas_7.html

.hword expressions

This expects zero or more expressions, and emits a 16 bit number for each.

This directive is a synonym for `.short'; depending on the target architecture,
it may also be a synonym for `.word'.

(caused marker struct layout discrepancy on ARM)

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>