libconfig++ is only a thin wrapper around libconfig. Because of the
use of exception handling this wrapper requires more memory than needed.
As we have our own wrapper (ConfigFile) just drop the C++ stuff.
A hard-coded path does not play nicely with a generic installer.
The installation path is now looked up in the registry with the
key SOFTWARE\\ldc-developers\\LDC\\<version>\\Path.
It is the responsibility of the installer to set this value.
1. Main include corresponding to .cpp file, if any.
2. DMD and LDC includes.
3. LLVM includes.
4. System includes.
Also updated a few include guards to match the default format.
