Where you have:

use v5.12;
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"Similarly, if the specified Perl version is greater than or equal to 5.12.0, strictures are enabled lexically as with use strict."(https://perldoc.pl/functions/use).

So to fix your code, use my:

while ( my ($key, $value) = each %count) {
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Returns:

pebbles => 1
dino => 1
wlima => 1
fred => 3
barney => 2
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The warnings that were printed are telling you what's wrong:

Global symbol "$key" requires explicit package name (did you forget to
+ declare "my $key"?) at - line 11.
Global symbol "$value" requires explicit package name (did you forget 
+to declare "my $value"?) at - line 11.
Global symbol "$key" requires explicit package name (did you forget to
+ declare "my $key"?) at - line 12.
Global symbol "$value" requires explicit package name (did you forget 
+to declare "my $value"?) at - line 12.
Execution of - aborted due to compilation errors.
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You need to declare those two variables, which is easy enough to do with while ( my ($key, $value) = each %count) {

showing the full code:

#! /usr/bin/perl
use v5.12;
use warnings;

## 2/15/19

     my @people = qw{ fred barney fred wlima dino barney fred pebbles 
+};
     my %count;    # new empty hash
     $count{$_}++ foreach @people;

     while ( my ($key, $value) = each %count) {
       print "$key => $value\n";
    }
__END__
__OUTPUT__
wlima => 1
barney => 2
dino => 1
fred => 3
pebbles => 1
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edit: the colon after the { looked like it was part of the code, started new paragraph instead.