It seems a couple (not too frequently used) parameters have changed in the SOURCES file, as of the Windows XP DDK. For example, to allow different flags for different targets, according to MAKEFILE.DEF:

xxx_warning_level

xxx_optimization

xxx_STDCALL = 1 use _stdcall calling convention 0 use _cdecl calling convention

xxx_cppflags

Where:

xxx_... is {MSC|386|axp64|alpha|MPPC|ia64|amd64} where MSC_ applies to the C8 compiler independent of the cpu type. Specific cpu_ will take precedence over the equivalent MSC_ variable. 

These replace other, earlier, parameters (such as NTCPPFLAGS).

Believe it or not, much of this is now documented in the DDK documentation set. So, if you haven't read the DDK doc set recently, you haven't read the DDK doc set at all.

Also, this highlights the importance of re-reading MAKEFILE.DEF from time to time. It changes.