#ifdef versus if for machine dependant code

eg:

	#ifdef CONFIG_MACH_VR1000
	       foo;
	#endif

or:

	if (machine_is_vr1000()) {
		foo;
	}

The advantages for using if are:

1) The code always get parsed by the compiler,
   thus ensuring that the compile has not been
   broken by any updates, making it easier to
   check any updates.

2) Kernels can be built to support more than
   one machine, which reduces that the number
   of builds to test a given kernel.

3) Modern compilers will throw away the code if
   they can deduce the result of the if at compile
   time, thus negating the problem of unused code
   being place into the output. 

   The machine_is_XXX() system will ensure that
   a false is given if the machine support is
   not being built into the kernel.

4) #if and #ifdef cause a bigger disruption to
   the code readability than the use of if.