Dockerfile: Update to LLVM 15

This commit updates the LLVM version from 12 to 15.

Signed-off-by: Stephanos Ioannidis <root@stephanos.io>

Dockerfile

@@ -4,7 +4,7 @@ ARG ZSDK_VERSION=0.15.0
 ARG DOXYGEN_VERSION=1.9.4
 ARG CMAKE_VERSION=3.20.5
 ARG RENODE_VERSION=1.13.1
-ARG LLVM_VERSION=12
+ARG LLVM_VERSION=15
 ARG BSIM_VERSION=v1.0.3
 ARG SPARSE_VERSION=9212270048c3bd23f56c20a83d4f89b870b2b26e
 ARG WGET_ARGS="-q --show-progress --progress=bar:force:noscroll --no-check-certificate"