[docker] Fix LLVM_EXTERNAL_PROJECTS cmake variable value

[azharudd]

Summary

LLVM_ENABLE_PROJECTS expects a semicolon separated project list.

Fixes PR38158.

[ilya-biryukov]

Wow, that's a huge oversight on my end.
Thanks for fixing this! LGTM

llvm/trunk/utils/docker/build_docker_image.sh

case "$1" in
     -p|--llvm-project)
       PROJ="$2"
       if [ "$PROJ" == "cfe" ]; then
         PROJ="clang"
       fi
 
       CHECKOUT_ARGS="$CHECKOUT_ARGS $1 $PROJ"
       if [ "$PROJ" != "clang-tools-extra" ]; then
-        CMAKE_ENABLED_PROJECTS="$CMAKE_ENABLED_PROJECTS:$PROJ"
+        CMAKE_ENABLED_PROJECTS="$CMAKE_ENABLED_PROJECTS;$PROJ"
       fi
 
       shift 2
       ;;
     -c|--checksums)
       shift
       CHECKSUMS_FILE="$1"
       shift
       ;;
     --)
       shift
       BUILDSCRIPT_ARGS="$BUILDSCRIPT_ARGS -- $*"
       SEEN_CMAKE_ARGS=1
       shift $#
       ;;
     *)
       echo "Unknown argument $1"
       exit 1
       ;;
   esac
 done
 
 
 if [ "$CMAKE_ENABLED_PROJECTS" != "" ]; then
-  # Remove the leading ':' character.
+  # Remove the leading ';' character.
   CMAKE_ENABLED_PROJECTS="${CMAKE_ENABLED_PROJECTS:1}"
 
   if [[ $SEEN_CMAKE_ARGS -eq 0 ]]; then
     BUILDSCRIPT_ARGS="$BUILDSCRIPT_ARGS --"
   fi
   BUILDSCRIPT_ARGS="$BUILDSCRIPT_ARGS -DLLVM_ENABLE_PROJECTS=$CMAKE_ENABLED_PROJECTS"
 fi