This option tells the compiler that the __regcall calling
convention should be used for functions that do not directly specify a calling
convention. This calling convention ensures that as many values as possible are
passed or returned in registers.
It ensures that __regcall is the default calling convention for functions in
the compilation, unless another calling convention is specified in a
This calling convention is ignored if it is specified for a function with
Note that all __regcall functions must have prototypes.