A few tips to get you going,
- Start here,
http://wiki.alliedmods.net/Porting_to_Left_4_Dead
- Use the hl2sdk-csgo @
http://hg.alliedmods.net/hl2sdks/hl2sdk-csgo
- Add COMPILER_MSVC and COMPILER_MSVC32 to your defines on Windows, and COMPILER_GCC on linux.
- Make sure to also link interfaces.lib/interfaces_i486.a, in addition to tier1.
I may do a wiki article for it at a later date. Most of this applies to the Alien Swarm engine as well, but that did not have a linux version.