I want to add the new mcu(Cortex M0 of ARM) in the Arduino IDE

I want to add the new mcu(Cortex M0 of ARM) in the Arduino IDE.
I downloaded the Source code of Arduino IDE.
I don't know how to modify.
Let me know how to modify about Arduino IDE.

Which board do you have that you’re trying to add support for? You don’t need to modify the IDE source code.

I'd think that a second installation of the IDE were the simplest solution, where the IDE uses the compiler and libraries of the ARM architecture.

The Microcontrollers forum may be a better place for your questions.

No second installation is necessary. The IDE is already set up to support other architectures by a simple Boards Manager installation process. The Arduino Zero is a Cortex M0+ and all you need to do to add support is Tools > Board > Boards Manager > Arduino SAMD Boards > Install. There are 3rd party hardware packages for other MCUs than the SAMD21, for those you only need to add the Boards Manager URL to File > Preferences > Additional Boards Manager URLs and then do the Boards Manager install process for that package.