random:cipher: handle substitution in sed command

* cipher/Makefile.am (o_flag_munging): Add 'g' flag for first sed
expression.
* random/Makefile.am (o_flag_munging): Likewise.

It was there earlier and accidentally removed from
Makefile.am of cipher and random

[jk: add changelog to commit message]

• Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>