Support for apple's M1

When I install Fastor (cmake .. & make) on a mac with M1 pro, I got the following error:

```
../Fastor/config/cpuid.h:48:18: error: invalid output constraint '=a' in asm
      ("cpuid" : "=a" (regs[0]), "=b" (regs[1]), "=c" (regs[2]), "=d" (regs[3])
```

I am using clang++ as the compiler.
