64 bit support

[bottiger1]

I updated ambuild files to support 64 bit compilation.

However I had to add a linux specific thing by creating a symlink to hl2sdk-manifest (a new sourcemod project containing game specific compile paths) due to ambuild not being able to run the hl2sdk-manifest script if it is outside the source path, and ambuild is not able to create symlinks outside the build path either.

The original author of the new 64bit ambuild script just copied the directory, but I think that is a bad solution.

This is inside the build/build bash script.