I can't reproduce this:

derick@singlemalt:~ $ php -v
PHP 7.0.21-dev (cli) (built: Jun  1 2017 14:07:31) ( NTS DEBUG )
Copyright (c) 1997-2017 The PHP Group
Zend Engine v3.0.0, Copyright (c) 1998-2017 Zend Technologies
    with Zend OPcache v7.0.21-dev, Copyright (c) 1999-2017, by Zend Technologies
    with Xdebug v2.5.5-dev, Copyright (c) 2002-2017, by Derick Rethans

derick@singlemalt:~ $ cat /tmp/74806.php 
<?php
$a = new DateTime('now', new DateTimeZone('Europe/Budapest')); 
var_dump($a);

derick@singlemalt:~ $ php /tmp/74806.php
/tmp/74806.php:3:
class DateTime#1 (3) {
  public $date =>
  string(26) "2017-06-23 15:12:18.000000"
  public $timezone_type =>
  int(3)
  public $timezone =>
  string(15) "Europe/Budapest"
}

Are you using the PHP that comes with Debian?
Or did you compile it yourself?
Did you install the timezonedb extension?
If so, which version?
What does "php --ri date" output?

cheers,
Derick

root@server:~/server-scripts/work# php -v
PHP 7.0.20-2 (cli) (built: Jun 14 2017 05:30:04) ( NTS )
Copyright (c) 1997-2017 The PHP Group
Zend Engine v3.0.0, Copyright (c) 1998-2017 Zend Technologies
    with Zend OPcache v7.0.20-2, Copyright (c) 1999-2017, by Zend Technologies

root@server:~/server-scripts/work# php --ri date

date

date/time support => enabled
"Olson" Timezone Database Version => 0.system
Timezone Database => internal
Default timezone => UTC

Directive => Local Value => Master Value
date.timezone => no value => no value
date.default_latitude => 31.7667 => 31.7667
date.default_longitude => 35.2333 => 35.2333
date.sunset_zenith => 90.583333 => 90.583333
date.sunrise_zenith => 90.583333 => 90.583333

root@server:~/server-scripts/work#  cat /tmp/74806.php 
<?php
$a = new DateTime('now', new DateTimeZone('Europe/Budapest')); 
var_dump($a);

root@server:~/server-scripts/work# php /tmp/74806.php

mmap() failed: [12] Cannot allocate memory

mmap() failed: [12] Cannot allocate memory
PHP Fatal error:  Out of memory (allocated 2097152) (tried to allocate 19301007360 bytes) in /tmp/74806.php on line 2
root@server:~/server-scripts/work# 


This is the default Debian Stretch with apt install.

root@server:~/server-scripts/work#  cat /tmp/74806.php 
<?php
$a = new DateTime('now', new DateTimeZone('Europe/Paris')); 
var_dump($a);
root@server:~/server-scripts/work# php /tmp/74806.php
object(DateTime)#1 (3) {
  ["date"]=>
  string(26) "2017-06-23 15:29:36.000000"
  ["timezone_type"]=>
  int(3)
  ["timezone"]=>
  string(12) "Europe/Paris"
}

OK. Closing this then. Debian patches PHP's date/time support. The default one doesn't use mmap, so this is entirely in their court. Please report this to the Debian project.

echo "<pre>";
echo "\ndate_default_timezone_get\n";
echo date_default_timezone_get();
echo "\n\ntimezone_version_get\n";
echo timezone_version_get();
echo "\n\ntimezone_identifiers_list\n";
echo print_r(timezone_identifiers_list());
echo "\n\ntimezone_abbreviations_list\n";
echo  print_r(timezone_abbreviations_list());
echo "\n\ntimezone_identifiers_list\n";
echo  print_r(timezone_identifiers_list());
echo "\n\ntimezone_location_get\n";
echo print_r(timezone_location_get(new \DateTimeZone('Europe/Budapest')));
echo "\n\n";


It shows that Europe/Budapest is there:
  [315] => Europe/Amsterdam
    [316] => Europe/Andorra
    [317] => Europe/Astrakhan
    [318] => Europe/Athens
    [319] => Europe/Belgrade
    [320] => Europe/Berlin
    [321] => Europe/Bratislava
    [322] => Europe/Brussels
    [323] => Europe/Bucharest
    [324] => Europe/Budapest
    [325] => Europe/Busingen
    [326] => Europe/Chisinau
    [327] => Europe/Copenhagen
    [328] => Europe/Dublin
    [329] => Europe/Gibraltar
    [330] => Europe/Guernsey
    [331] => Europe/Helsinki
    [332] => Europe/Isle_of_Man
    [333] => Europe/Istanbul
    [334] => Europe/Jersey
    [335] => Europe/Kaliningrad
    [336] => Europe/Kiev
    [337] => Europe/Kirov
    [338] => Europe/Lisbon
    [339] => Europe/Ljubljana
    [340] => Europe/London
    [341] => Europe/Luxembourg
    [342] => Europe/Madrid
    [343] => Europe/Malta
    [344] => Europe/Mariehamn
    [345] => Europe/Minsk
    [346] => Europe/Monaco
    [347] => Europe/Moscow
    [348] => Europe/Oslo
    [349] => Europe/Paris
    [350] => Europe/Podgorica
    [351] => Europe/Prague
    [352] => Europe/Riga
    [353] => Europe/Rome
    [354] => Europe/Samara
    [355] => Europe/San_Marino
    [356] => Europe/Sarajevo
    [357] => Europe/Saratov
    [358] => Europe/Simferopol
    [359] => Europe/Skopje
    [360] => Europe/Sofia
    [361] => Europe/Stockholm
    [362] => Europe/Tallinn
    [363] => Europe/Tirane
    [364] => Europe/Ulyanovsk
    [365] => Europe/Uzhgorod
    [366] => Europe/Vaduz
    [367] => Europe/Vatican
    [368] => Europe/Vienna
    [369] => Europe/Vilnius
    [370] => Europe/Volgograd
    [371] => Europe/Warsaw
    [372] => Europe/Zagreb
    [373] => Europe/Zaporozhye
    [374] => Europe/Zurich

 [15] => Array
                (
                    [dst] => 
                    [offset] => 3600
                    [timezone_id] => Europe/Budapest
                )

Fatal error:  Allowed memory size of 134217728 bytes exhausted (tried to allocate 19301007360 bytes) in /var/www/test.patrikx3.tk/public/index.php on line 14

Yes, it is there. This is a bug in the Debian specific patch that they made regarding timezones. Please file a bug report with the Debian project and please do not reopen this report again.