fix: string constants (-Wwrite-strings)

Do not use an anonymous string literal with a non-const char pointer as
this will discard the implicit const, use static non-const string
instead when appropriate. Otherwise, we could end up trying to write to
a string constant.

Change-Id: Ie2bb0e5ab7978930f9edcdb379bd181caaacc15c
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>