detect-virt: do not try to read all of /proc/cpuinfo
    
    Quoting https://github.com/systemd/systemd/issues/10074:
    > detect_vm_uml() reads /proc/cpuinfo with read_full_file()
    > read_full_file() has a file max limit size of READ_FULL_BYTES_MAX=(4U*1024U*1024U)
    > Unfortunately, the size of my /proc/cpuinfo is bigger, approximately:
    > echo $(( 4* $(cat /proc/cpuinfo | wc -c)))
    > 9918072
    > This causes read_full_file() to fail and the Condition test fallout.
    
    Let's just read line by line until we find an intersting line. This also
    helps if not running under UML, because we avoid reading as much data.
    
    (cherry picked from commit 6058516a14ada1748313af6783f5b4e7e3006654)
    
    Resolves: #1631532
    
    patch_name: 0045-detect-virt-do-not-try-to-read-all-of-proc-cpuinfo.patch
    present_in_specfile: true
    location_in_specfile: 45
    squash_commits: true