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>
build: add LLVM include dir explicitly to make build bot happy

For some reason build bot's llvm-config --cppflags does not return the
LLVM's main include dir. Add it explicitly for now.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@iki.fi>
build: be even more explicit with the include dir...

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@iki.fi>
build: add debug print