Add well known types to php runtime. (#3697)

* Add well known types to php runtime.

* Fix php7.0 tests

* No longer generate empty.proto in test as it has been included in
runtime.

* Fix zts build

* Clean code

* Rename g_p_b_empty to empty.

* Don't generate code for empty.proto in compatibility test

* Fix 32-bit

* Fix mac build

* Fix Makefile.am to add new files
diff --git a/php/src/Google/Protobuf/Value.php b/php/src/Google/Protobuf/Value.php
new file mode 100644
index 0000000..052a377
--- /dev/null
+++ b/php/src/Google/Protobuf/Value.php
@@ -0,0 +1,194 @@
+<?php
+# Generated by the protocol buffer compiler.  DO NOT EDIT!
+# source: google/protobuf/struct.proto
+
+namespace Google\Protobuf;
+
+use Google\Protobuf\Internal\GPBType;
+use Google\Protobuf\Internal\RepeatedField;
+use Google\Protobuf\Internal\GPBUtil;
+
+/**
+ * `Value` represents a dynamically typed value which can be either
+ * null, a number, a string, a boolean, a recursive struct value, or a
+ * list of values. A producer of value is expected to set one of that
+ * variants, absence of any variant indicates an error.
+ * The JSON representation for `Value` is JSON value.
+ *
+ * Generated from protobuf message <code>google.protobuf.Value</code>
+ */
+class Value extends \Google\Protobuf\Internal\Message
+{
+    protected $kind;
+
+    public function __construct() {
+        \GPBMetadata\Google\Protobuf\Struct::initOnce();
+        parent::__construct();
+    }
+
+    /**
+     * Represents a null value.
+     *
+     * Generated from protobuf field <code>.google.protobuf.NullValue null_value = 1;</code>
+     * @return int
+     */
+    public function getNullValue()
+    {
+        return $this->readOneof(1);
+    }
+
+    /**
+     * Represents a null value.
+     *
+     * Generated from protobuf field <code>.google.protobuf.NullValue null_value = 1;</code>
+     * @param int $var
+     * @return $this
+     */
+    public function setNullValue($var)
+    {
+        GPBUtil::checkEnum($var, \Google\Protobuf\NullValue::class);
+        $this->writeOneof(1, $var);
+
+        return $this;
+    }
+
+    /**
+     * Represents a double value.
+     *
+     * Generated from protobuf field <code>double number_value = 2;</code>
+     * @return float
+     */
+    public function getNumberValue()
+    {
+        return $this->readOneof(2);
+    }
+
+    /**
+     * Represents a double value.
+     *
+     * Generated from protobuf field <code>double number_value = 2;</code>
+     * @param float $var
+     * @return $this
+     */
+    public function setNumberValue($var)
+    {
+        GPBUtil::checkDouble($var);
+        $this->writeOneof(2, $var);
+
+        return $this;
+    }
+
+    /**
+     * Represents a string value.
+     *
+     * Generated from protobuf field <code>string string_value = 3;</code>
+     * @return string
+     */
+    public function getStringValue()
+    {
+        return $this->readOneof(3);
+    }
+
+    /**
+     * Represents a string value.
+     *
+     * Generated from protobuf field <code>string string_value = 3;</code>
+     * @param string $var
+     * @return $this
+     */
+    public function setStringValue($var)
+    {
+        GPBUtil::checkString($var, True);
+        $this->writeOneof(3, $var);
+
+        return $this;
+    }
+
+    /**
+     * Represents a boolean value.
+     *
+     * Generated from protobuf field <code>bool bool_value = 4;</code>
+     * @return bool
+     */
+    public function getBoolValue()
+    {
+        return $this->readOneof(4);
+    }
+
+    /**
+     * Represents a boolean value.
+     *
+     * Generated from protobuf field <code>bool bool_value = 4;</code>
+     * @param bool $var
+     * @return $this
+     */
+    public function setBoolValue($var)
+    {
+        GPBUtil::checkBool($var);
+        $this->writeOneof(4, $var);
+
+        return $this;
+    }
+
+    /**
+     * Represents a structured value.
+     *
+     * Generated from protobuf field <code>.google.protobuf.Struct struct_value = 5;</code>
+     * @return \Google\Protobuf\Struct
+     */
+    public function getStructValue()
+    {
+        return $this->readOneof(5);
+    }
+
+    /**
+     * Represents a structured value.
+     *
+     * Generated from protobuf field <code>.google.protobuf.Struct struct_value = 5;</code>
+     * @param \Google\Protobuf\Struct $var
+     * @return $this
+     */
+    public function setStructValue($var)
+    {
+        GPBUtil::checkMessage($var, \Google\Protobuf\Struct::class);
+        $this->writeOneof(5, $var);
+
+        return $this;
+    }
+
+    /**
+     * Represents a repeated `Value`.
+     *
+     * Generated from protobuf field <code>.google.protobuf.ListValue list_value = 6;</code>
+     * @return \Google\Protobuf\ListValue
+     */
+    public function getListValue()
+    {
+        return $this->readOneof(6);
+    }
+
+    /**
+     * Represents a repeated `Value`.
+     *
+     * Generated from protobuf field <code>.google.protobuf.ListValue list_value = 6;</code>
+     * @param \Google\Protobuf\ListValue $var
+     * @return $this
+     */
+    public function setListValue($var)
+    {
+        GPBUtil::checkMessage($var, \Google\Protobuf\ListValue::class);
+        $this->writeOneof(6, $var);
+
+        return $this;
+    }
+
+    /**
+     * @return string
+     */
+    public function getKind()
+    {
+        return $this->whichOneof("kind");
+    }
+
+}
+