Replace hardcoded library name with find_library()

Instead of merely adding "rt" to the link libraries use find_library()
to find librt and link with the result if found.
Upgrade to CMake 2.8.12
Remove tweak number from full version
Don't add -m32 to compile flags
Drop NSIS support
Manually set CPack generator and package filename
Don't bother with the PDB file
Don't make helloworld search for SDK

It's already found at the parent level!