imsettings: fix build error.

multi-line ACLOCAL_AMFLAGS isn't supported by autoreconf, otherwise
a configure error as follow will be caught.

  aclocal: error: non-option arguments are not accepted: '\'.

Signed-off-by: Bian Naimeng <biannm@cn.fujitsu.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>