Install llvm15 to compile CppInterOp on osx15 cling jobs

Author: mcbarton

.github/workflows/ci.yml

@@ -294,8 +294,15 @@ jobs:
           echo "SDKROOT=$(xcrun --sdk macosx --show-sdk-path)" >> $GITHUB_ENV
           export ARCHITECHURE=$(uname -m)
           if [[ "$ARCHITECHURE" == "arm64" ]]; then
-            echo "CC=$(brew --prefix llvm@18)/bin/clang" >> $GITHUB_ENV
-            echo "CXX=$(brew --prefix llvm@18)/bin/clang++" >> $GITHUB_ENV
+            cling_on=$(echo "${{ matrix.cling }}" | tr '[:lower:]' '[:upper:]')
+            if [[ "${cling_on}" == "ON" ]]; then  
+                brew install llvm@15
+                echo "CC=$(brew --prefix llvm@15)/bin/clang" >> $GITHUB_ENV
+                echo "CXX=$(brew --prefix llvm@15)/bin/clang++" >> $GITHUB_ENV
+            else
+              echo "CC=$(brew --prefix llvm@18)/bin/clang" >> $GITHUB_ENV
+              echo "CXX=$(brew --prefix llvm@18)/bin/clang++" >> $GITHUB_ENV
+            fi
           else
             echo "CC=$(brew --prefix llvm@15)/bin/clang" >> $GITHUB_ENV
             echo "CXX=$(brew --prefix llvm@15)/bin/clang++" >> $GITHUB_ENV
@@ -767,8 +774,15 @@ jobs:
           echo "SDKROOT=$(xcrun --sdk macosx --show-sdk-path)" >> $GITHUB_ENV
           export ARCHITECHURE=$(uname -m)
           if [[ "$ARCHITECHURE" == "arm64" ]]; then
-            echo "CC=$(brew --prefix llvm@18)/bin/clang" >> $GITHUB_ENV
-            echo "CXX=$(brew --prefix llvm@18)/bin/clang++" >> $GITHUB_ENV
+            cling_on=$(echo "${{ matrix.cling }}" | tr '[:lower:]' '[:upper:]')
+            if [[ "${cling_on}" == "ON" ]]; then  
+                brew install llvm@15
+                echo "CC=$(brew --prefix llvm@15)/bin/clang" >> $GITHUB_ENV
+                echo "CXX=$(brew --prefix llvm@15)/bin/clang++" >> $GITHUB_ENV
+            else
+              echo "CC=$(brew --prefix llvm@18)/bin/clang" >> $GITHUB_ENV
+              echo "CXX=$(brew --prefix llvm@18)/bin/clang++" >> $GITHUB_ENV
+            fi
           else
             echo "CC=$(brew --prefix llvm@15)/bin/clang" >> $GITHUB_ENV
             echo "CXX=$(brew --prefix llvm@15)/bin/clang++" >> $GITHUB_ENV