libliftoff is untagged and has no other consumers. Keep it private to
gamescope package for now.

--- subprojects/libliftoff/meson.build.orig	2020-05-26 19:30:31 UTC
+++ subprojects/libliftoff/meson.build
@@ -38,7 +38,7 @@ liftoff_lib = library(
 	include_directories: liftoff_inc,
 	version: meson.project_version(),
 	dependencies: liftoff_deps,
-	install: true,
+	install: not meson.is_subproject(),
 )
 
 liftoff = declare_dependency(
@@ -47,6 +47,7 @@ liftoff = declare_dependency(
 	dependencies: liftoff_deps,
 )
 
+if not meson.is_subproject()
 install_headers('include/libliftoff.h')
 
 pkgconfig = import('pkgconfig')
@@ -60,3 +61,4 @@ pkgconfig.generate(
 
 subdir('example')
 subdir('test')
+endif