String::toInt() and atol() behave different on different platforms with a number that is too large.

User axemaster found strange behavior when using String::toInt() with a number that is too large. See the topic in the Arduino forum: [https://forum.arduino.cc/t/toint-bug-how-unfortunate/1041669](https://forum.arduino.cc/t/toint-bug-how-unfortunate/1041669).
The result is different for 8-bit and 32-bit platforms.
It was narrowed down to the undefined behaviour of atol() when a number is too large to fit in a long.

The atol() in String::toInt() in String.cpp could be replaced by strtol() followed by a check for LONG_MAX or LONG_MIN and return zero if that happens. The documentation can stay as it is, because it will return a long, and zero if something is wrong.
To allow LONG_MAX and LONG_MIN as valid input numbers, the errno has to be used. I don't know how that will hold up in a multitasking environment.

从 String.cpp 中的 String::toInt() 开始，检查 atol() 对超出平台 long 范围的值的行为。在 8-bit 和 32-bit 平台之间比较提议的 strtol() 及 errno 处理方式；当超大输入能够产生一致且有文档说明的结果，并且不会错误处理 LONG_MAX 或 LONG_MIN 时，该 issue 即完成。

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