build: new build for LLVM related stuff

Use llvm-config to find out preprocessor flags, needed libs, etc.
Separate LLVM builds can be used for release and debug.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@iki.fi>
build: remove unused StaticLinksOpt()

The function is not used anymore, so remove it.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@iki.fi>