Refactor LLVM installation and environment setup

Author: mcbarton

.github/workflows/MacOS.yml

@@ -125,28 +125,13 @@ jobs:
           echo "CC=gcc-${vers}" >> $GITHUB_ENV
           echo "CXX=g++-${vers}" >> $GITHUB_ENV
         else
-          export ARCHITECHURE=$(uname -m)
-          if [[ "$ARCHITECHURE" == "arm64" ]]; then
-            cling_on=$(echo "${{ matrix.cling }}" | tr '[:lower:]' '[:upper:]')
-            if [[ "${cling_on}" == "ON" ]]; then  
-                brew install llvm@15
-                brew remove llvm@18
-                brew cleanup
-                #FIXME: Do not believe setting all these environment variables are necessary
-                #       They were set to avoid using Xcodes libc++ and to stop CppInterOp using llvm@18 in tests
-                echo 'LDFLAGS="-L/opt/homebrew/opt/llvm@15/lib/ -L/opt/homebrew/opt/llvm@15/c++/"' >> $GITHUB_ENV
-                echo 'CPPFLAGS="-I/opt/homebrew/opt/llvm@15/include"' >> $GITHUB_ENV
-                echo 'CPATH="/opt/homebrew/include/"' >> $GITHUB_ENV
-                echo 'LIBRARY_PATH="/opt/homebrew/lib/"' >> $GITHUB_ENV
-                echo "CC=$(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++" >> $GITHUB_ENV
-            fi
+          brew install llvm@15
+          if [[ "$(uname -m)" == "x86_64" ]]; then
+            echo "CC=/usr/local/opt/llvm@15/bin/clang" >> $GITHUB_ENV
+            echo "CXX=/usr/local/opt/llvm@15/bin/clang++" >> $GITHUB_ENV
           else
-            echo "CC=$(brew --prefix llvm@15)/bin/clang" >> $GITHUB_ENV
-            echo "CXX=$(brew --prefix llvm@15)/bin/clang++" >> $GITHUB_ENV
+            echo "CC=/opt/homebrew/opt/llvm@15/bin/clang" >> $GITHUB_ENV
+            echo "CXX=/opt/homebrew/opt/llvm@15/bin/clang++" >> $GITHUB_ENV
           fi
         fi
         echo "SDKROOT=$(xcrun --sdk macosx --show-sdk-path)" >> $GITHUB_ENV