C++/C Code to have different execution block on M1 and Intel

  apple-m1, c++

I am writing a code for macOS application.
The application would be running on M1 based Macs as well as Intel based Macs also.
What would be the switch to differentiate M1 and Intel?

if (M1)
   do something for M1
else if (Intel)
   do something for Intel

Source: Windows Questions C++