add clad (a clang plugin) (#80)

* add clad (a cland plugin)

Adds the ability to build llvm external projects along with clang/llvm

* updates according to code review

build/build.sh

@@ -17,6 +17,9 @@ NINJA_TARGET=install
 NINJA_TARGET_RUNTIMES=install-runtimes
 TAG=
 declare -a PATCHES_TO_APPLY
+EXTERNAL_PROJECT_DIR=${ROOT}/external
+declare -a EXTERNAL_PROJECT_URLS
+declare -a LLVM_EXTERNAL_PROJECTS_LIST
 
 case $VERSION in
 ce-trunk)
@@ -334,6 +337,12 @@ mlir-*)
         if [[ $MAJOR -ge 18 ]]; then
             CMAKE_EXTRA_ARGS+=("-DLIBCXX_INSTALL_MODULES=ON")
         fi
+
+        if [[ $MAJOR -eq 18 ]]; then
+            EXTERNAL_PROJECT_URLS+=("https://github.com/vgvassilev/clad.git")
+            LLVM_EXTERNAL_PROJECTS_LIST+=("clad")
+            CMAKE_EXTRA_ARGS+=("-DLLVM_EXTERNAL_CLAD_SOURCE_DIR=${EXTERNAL_PROJECT_DIR}/clad")
+        fi
         ;;
     esac
     ;;
@@ -383,6 +392,16 @@ for PATCH_TO_APPLY in "${PATCHES_TO_APPLY[@]}"; do
     git -C "${ROOT}/llvm-project" apply "${PATCH_TO_APPLY}" -v
 done
 
+# Setup external projects
+mkdir -p "${EXTERNAL_PROJECT_DIR}"
+for LLVM_EXTERNAL_PROJECT in "${!EXTERNAL_PROJECT_URLS[@]}"; do
+    git clone --depth 1 "${EXTERNAL_PROJECT_URLS[LLVM_EXTERNAL_PROJECT]}" "${EXTERNAL_PROJECT_DIR}/${LLVM_EXTERNAL_PROJECTS_LIST[LLVM_EXTERNAL_PROJECT]}"
+done
+LLVM_EXTERNAL_PROJECTS=
+for LLVM_EXTERNAL_PROJECT in "${LLVM_EXTERNAL_PROJECTS_LIST}"; do
+    LLVM_EXTERNAL_PROJECTS+="${LLVM_EXTERNAL_PROJECT};";
+done
+
 # For older LLVM versions, merge runtime and projects
 # August 2021 is when bootstrapping become necessary, bootstrapping might have been supported previously a few years prior
 COMMIT_DATE=$(cd "${ROOT}/llvm-project/llvm" && git show -s --format=%ct HEAD)
@@ -413,6 +432,7 @@ cmake \
     -G "Ninja" "${ROOT}/llvm-project/llvm" \
     -DLLVM_ENABLE_PROJECTS="${LLVM_ENABLE_PROJECTS}" \
     -DLLVM_ENABLE_RUNTIMES="${LLVM_ENABLE_RUNTIMES}" \
+    -DLLVM_EXTERNAL_PROJECTS="${LLVM_EXTERNAL_PROJECTS}" \
     -DCMAKE_BUILD_TYPE:STRING=Release \
     -DCMAKE_INSTALL_PREFIX:PATH="${STAGING_DIR}" \
     -DCMAKE_C_COMPILER:PATH="/opt/compiler-explorer/gcc-${GCC_VERSION}/bin/gcc" \