[run-tests.php] Replace backtick operator string literals with shell_exec() calls

The rationale is that `shell_exec()` is identical to the backtick operator (both of which are disabled when `shell_exec` function is disabled) makes it very clear that it is a shell execution, and eases security audits too.

Author: Ayesh

run-tests.php

@@ -843,19 +843,19 @@ function write_information(): void
     $info_params = [];
     settings2array($ini_overwrites, $info_params);
     $info_params = settings2params($info_params);
-    $php_info = `$php $pass_options $info_params $no_file_cache "$info_file"`;
-    define('TESTED_PHP_VERSION', `$php -n -r "echo PHP_VERSION;"`);
+    $php_info = shell_exec("$php $pass_options $info_params $no_file_cache \"$info_file\"");
+    define('TESTED_PHP_VERSION', shell_exec("$php -n -r \"echo PHP_VERSION;\""));
 
     if ($php_cgi && $php != $php_cgi) {
-        $php_info_cgi = `$php_cgi $pass_options $info_params $no_file_cache -q "$info_file"`;
+        $php_info_cgi = shell_exec("$php_cgi $pass_options $info_params $no_file_cache -q \"$info_file\"");
         $php_info_sep = "\n---------------------------------------------------------------------";
         $php_cgi_info = "$php_info_sep\nPHP         : $php_cgi $php_info_cgi$php_info_sep";
     } else {
         $php_cgi_info = '';
     }
 
     if ($phpdbg) {
-        $phpdbg_info = `$phpdbg $pass_options $info_params $no_file_cache -qrr "$info_file"`;
+        $phpdbg_info = shell_exec("$phpdbg $pass_options $info_params $no_file_cache -qrr \"$info_file\"");
         $php_info_sep = "\n---------------------------------------------------------------------";
         $phpdbg_info = "$php_info_sep\nPHP         : $phpdbg $phpdbg_info$php_info_sep";
     } else {
@@ -883,7 +883,7 @@ function write_information(): void
         }
         ?>
     PHP);
-    $exts_to_test = explode(',', `$php $pass_options $info_params $no_file_cache "$info_file"`);
+    $exts_to_test = explode(',', shell_exec("$php $pass_options $info_params $no_file_cache \"$info_file\""));
     // check for extensions that need special handling and regenerate
     $info_params_ex = [
         'session' => ['session.auto_start=0'],
@@ -3652,8 +3652,8 @@ public function getExtensions(string $php): array
             return $this->extensions[$php];
         }
 
-        $extDir = `$php -d display_errors=0 -r "echo ini_get('extension_dir');"`;
-        $extensions = explode(",", `$php -d display_errors=0 -r "echo implode(',', get_loaded_extensions());"`);
+        $extDir = shell_exec("$php -d display_errors=0 -r \"echo ini_get('extension_dir');\"");
+        $extensions = explode(",", shell_exec("$php -d display_errors=0 -r \"echo implode(',', get_loaded_extensions());\""));
         $extensions = array_map('strtolower', $extensions);
         if (in_array('zend opcache', $extensions)) {
             $extensions[] = 'opcache';