fontconfig fails to build from source on musl, because it does not
correctly detect availability of gettext. As a result, it does not
generate locales and fails dh_install due to missing files.

The root cause is a bug in the gettext detection macro. The problem is
fixed there, but fontconfig selects an older version that still contains
the problem.

Please update the version of the gettext macro to fix the detection. I'm
attaching a patch for your convenience.

Helmut