Fixed compilation on macOS arm64

[amv-bamboo]

Had the similar issue as in #167, but on the newer system:

mkdir -p build/common
mkdir -p build/zend
c++ -Wall -c -std=c++11 -fvisibility=hidden -DBUILDING_PHPCPP -Wno-write-strings -MD -fpic `php-config --includes` -g -o build/zend/base.o zend/base.cpp
In file included from zend/base.cpp:8:
In file included from zend/includes.h:134:
zend/hashiterator.h:75:32: warning: 'clone' overrides a member function but is not marked 'override' [-Winconsistent-missing-override]
    virtual ValueIteratorImpl *clone()
                               ^
zend/valueiteratorimpl.h:37:32: note: overridden virtual function is here
    virtual ValueIteratorImpl *clone() = 0;
                               ^
In file included from zend/base.cpp:8:
In file included from zend/includes.h:135:
zend/invaliditerator.h:26:32: warning: 'clone' overrides a member function but is not marked 'override' [-Winconsistent-missing-override]
    virtual ValueIteratorImpl *clone()
                               ^
zend/valueiteratorimpl.h:37:32: note: overridden virtual function is here
    virtual ValueIteratorImpl *clone() = 0;
                               ^
zend/base.cpp:280:12: error: conversion from 'long' to 'Php::Value' is ambiguous
    return countable->count();
           ^~~~~~~~~~~~~~~~~~
zend/../include/value.h:55:5: note: candidate constructor
    Value(int16_t value);
    ^
zend/../include/value.h:56:5: note: candidate constructor
    Value(int32_t value);
    ^
zend/../include/value.h:57:5: note: candidate constructor
    Value(int64_t value);
    ^
zend/../include/value.h:58:5: note: candidate constructor
    Value(bool value);
    ^
zend/../include/value.h:60:5: note: candidate constructor
    Value(char value);
    ^
zend/../include/value.h:64:5: note: candidate constructor
    Value(double value);
    ^
2 warnings and 1 error generated.
make: *** [build/zend/base.o] Error 1

Applied a fix with the type conversion suggested in the issue, seems to work