The problem is with qw because it does not interpolate the $savefile variable. See Quote and Quote like Operators. You can prove this as follows:

use strict; 
use warnings; 
use Data::Dumper; 
my $savefile='//depot/perl/files/scripts/file.c';
my $cmd = [ qw(p4 where $savefile) ];
print Dumper($cmd);
print ref($cmd), "\n";

__END__

$VAR1 = [
          'p4',
          'where',
          '$savefile'
        ];
ARRAY
[download]

You could try this instead:

my $savefile='//depot/perl/files/scripts/file.c';
my $cmd = [ (qw(p4 where), $savefile) ];
print Dumper($cmd);
print ref($cmd), "\n";

__END__

$VAR1 = [
          'p4',
          'where',
          '//depot/perl/files/scripts/file.c'
        ];
ARRAY
[download]