pangomm: Add missing dependency on pango

Fixes errors like

| configure:15678: error: Package requirements (glibmm-2.4 >= 2.14.1
cairomm-1.0 >= 1.2.2 pangocairo >= 1.23.0) were not met:
|
| No package 'pangocairo' found

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Acked-by: Andreas Müller <schnitzeltony@googlemail.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>