Optimise use of hardware under Mac + Windows in virtual machine
Compiling takes CPU even if pure OSX so in a VM will take all the CPU. Fan working and hot is not an issue - it will happen (try compiling gcc under OSX on an i7 CPU all 8 threads will be running for several minutes) I would although give more memory to the VM

To see what is taking CPU you need to look at Activity Monitor in OSX (which will show Parallels taking up a lot of CPU) and Task Manager(I might have forgotten the correct name) in Windows to show what the VM is spending its time on