[OpenMP][Docs] Updated the faq about building an OpenMP offloading capable compiler

After some issues about building runtimes along with LLVM were fixed,
building an OpenMP offloading capable compiler is pretty simple. This patch updates
the FAQ part in the doc.

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D93671

GitOrigin-RevId: 612ddc3117ce7715a3634fa0e0c5c6cdd3619d6b
1 file changed