>perl -wMstrict -le
"my $x;
 BEGIN {
   my $m = `uname -m`;
   print qq{m '$m'} if $m =~ /x86/;
   $x = 1 if $m =~ /x86/;
   use constant FOO => ($x ? 'true' : 'false');
   }
 print FOO;
 print qq{x '$x'};
"
m 'x86
'
false
x '1'

##</code><code>##

>perl -wMstrict -le
"BEGIN {
   use constant X   => (`uname -m` =~ /x86/) ? 1 : 0;
   use constant FOO => (X ? 'true' : 'false');
   }
 print FOO;
 print q{X '}, X, q{'};
"
true
X '1'

##</code><code>##

>perl -wMstrict -le
"my $x;
 BEGIN {
   my $m = `uname -m`;
   print qq{m '$m'} if $m =~ /x86/;
   $x = 1 if $m =~ /x86/;
   }
 use constant FOO => ($x ? 'true' : 'false');
 print FOO;
 print qq{x '$x'};
"
m 'x86
'
true
x '1'