java/openjdk11: remove custom LLVM - build with LLVM from base

Segfaults are no longer observed with current versions of LLVM 17 and 18
in base 13.3 and 14.1, so there is no need to pull such an old version
from ports to build.
For example build java/openjdk11 with LLVM from base and then build
java/eclipse and java/openjfx14 using java/openjdk11: build and run
without errors.

PR: 280056 260319
Approved by: java (maintainer, timeout 14 days)

(cherry picked from commit 08cc50220f1d71f12d13d7e2c957a5679b02914d)