.func name[,label].func emits debugging information to denote function name, and
is ignored unless the file is assembled with debugging enabled.
Only --gstabs[+] is currently supported.
label is the entry point of the function and if omitted name
prepended with the leading char is used.
leading char is usually _ or nothing, depending on the target.
All functions are currently defined to have void return type.
The function must be terminated with .endfunc.