minor #38818 Disable platform checks (nicolas-grekas)

This PR was merged into the 3.4 branch.

Discussion
----------

Disable platform checks

| Q             | A
| ------------- | ---
| Branch?       | 3.4
| Bug fix?      | no
| New feature?  | no
| Deprecations? | no
| Tickets       | Fix #38803
| License       | MIT
| Doc PR        | -

Let's see

Commits
-------

1d09b49076 Disable platform checks

.appveyor.yml

@@ -64,7 +64,6 @@ install:
     - php composer.phar config --global platform.php 5.5.9
     - php composer.phar update --no-progress --ansi
     - php phpunit install
-    - break > .phpunit/phpunit-4.8-0/vendor/composer/platform_check.php
 
 test_script:
     - SET X=0

.github/composer-config.json

@@ -1,5 +1,6 @@
 {
     "config": {
+        "platform-check": false,
         "preferred-install": {
             "symfony/form": "source",
             "symfony/http-kernel": "source",

.travis.yml

@@ -312,7 +312,6 @@ install:
               tfold src/Symfony/Component/Console.tty $PHPUNIT src/Symfony/Component/Console --group tty
               if [[ $PHP = ${MIN_PHP%.*} ]]; then
                   export PHP=$MIN_PHP
-                  echo '' > vendor/composer/platform_check.php
                   echo -e "1\\n0" | xargs -I{} bash -c "tfold src/Symfony/Component/Process.sigchild{} SYMFONY_DEPRECATIONS_HELPER=weak ENHANCE_SIGCHLD={} php-$MIN_PHP/sapi/cli/php .phpunit/phpunit-4.8-1/phpunit --colors=always src/Symfony/Component/Process/"
               fi
           fi