Fix up libadwaita to build with it. Update the command explanation to
allow building it with Qt-5. Also fix the errors detected in
org.linuxfromscratch.lfs.xml reported by "appstreamcli validate".
It fixes the "Operating System Details" content in appstreamcli sysinfo
output.
Note that the file name is derived from HOME_URL and ID properties from
/etc/os-release, and the HOME_URL property is just added (at LFS
r12.0-44). If HOME_URL is not set, the file should be renamed to
"lfs.xml" and the <id> in the file should be "lfs", instead of
"org.linuxfromscratch.lfs".