"sysgen_" dependency for Windows CE

CE build modules based on the "sysgen_" setting. Sometimes, some special sysgens will be set automatically by building tools. For example, sysgen_ppp will be added automatically if sysgen_l2tp is set. Build tools implement the functionality like this:

in public/cebase/oak/misc/***.bat

if "%SYSGEN_L2TP%"=="1" set SYSGEN_IPHLPAPI=1 if "%SYSGEN_L2TP%"=="1" set SYSGEN_PPP=1 if "%SYSGEN_L2TP%"=="1" set SYSGEN_WINSOCK=1 if "%SYSGEN_L2TP%"=="1" set SYSGEN_IPSEC=1 if "%SYSGEN_L2TP%"=="1" set SYSGEN_NET_WFP=1//...//... if "%SYSGEN_L2TP%"=="1" set CE_MODULES=%CE_MODULES% l2tp

You can see, 5 sysgens will be added as soon as sysgen_l2tp is set.  And it also defined l2tp as one of the CE_MODULES.