I believe you are missing a build dependency to supply the missing program.
It appears that you could add the package libglib2.0-bin to your build dependencies to make the program glib-compile-schemas available at build time. Apparently the program is used with Gsettings. The launchpad build process installs just the most basic packages, build dependencies declared in your debian/control file, and their dependencies, before trying to do the build.
If a build dependency is missing from the debian/control file an error is supposed to result as an aid to getting the build-dependencies correct.
To answer this, I noted the missing file, entered the command
locate glib-compile-schemas and
whereis glib-compile-schemas to find the missing file, and executed the command
dpkg -S glib-compile-schemas to find the name of the missing package.
If you don't want to compile schemas as part of the build process you will need to adjust the build process by changing debian/rules or the packages make files.