build: use llvm-config to find out libs

Use llvm-config to find out needed LLVM libraries.

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>
docs: update build instructions in GettingStarted.md

Update build instructions in GettingStarted.md.

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