require bcmath

bcmath (specifically, the bccomp function) is internally required, and tests fail if it's not available

php/composer.json

@@ -6,7 +6,8 @@
   "homepage": "https://developers.google.com/protocol-buffers/",
   "license": "BSD-3-Clause",
   "require": {
-    "php": ">=7.0.0"
+    "php": ">=7.1.0",
+    "ext-bcmath": "*"
   },
   "require-dev": {
     "phpunit/phpunit": ">=5.0.0"

php/src/Google/Protobuf/Internal/GPBUtil.php

@@ -37,6 +37,7 @@ use Google\Protobuf\FieldMask;
 use Google\Protobuf\Internal\GPBType;
 use Google\Protobuf\Internal\RepeatedField;
 use Google\Protobuf\Internal\MapField;
+use function bccomp;
 
 function camel2underscore($input) {
     preg_match_all(