Log Message:
Update pangomm to 2.24.0.

2.24.0:
(Skipped version numbers since 2.14.1, to match pango 1.24
(apart from the first digit, which we can't decrease.)

* Layout: Added show_in_cairo_context().
  (Louis-Francis Ratté-Boulianne) Bug #560232.
* Build: Allow pangomm to build outside the source tree. Bug #570322
  (Theppitak Karoonboonyanan)
* License Header consistency. (Deng Xiyue)