Using llvm 18 for compilation. (due to moving osx arm jobs to osx 15)

Author: mcbarton

.github/workflows/ci.yml

@@ -292,11 +292,13 @@ jobs:
           echo "CXX=g++-${vers}" >> $GITHUB_ENV
         else
           echo "SDKROOT=$(xcrun --sdk macosx --show-sdk-path)" >> $GITHUB_ENV
-          #Use clang-15 and clang++-15 compiler that is installed on runner, instead of one
-          #provided by MacOS (could brew install clang-16/17 to use consistent version
-          #of clang)
-          echo "CC=$(brew --prefix llvm@15)/bin/clang" >> $GITHUB_ENV
-          echo "CXX=$(brew --prefix llvm@15)/bin/clang++" >> $GITHUB_ENV
+          if [[ "$ARCHITECHURE" != "x86_64" ]]; then
+            echo "CC=$(brew --prefix llvm@18)/bin/clang" >> $GITHUB_ENV
+            echo "CXX=$(brew --prefix llvm@18)/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
+          fi
         fi
       env:
         compiler: ${{ matrix.compiler }}
@@ -762,11 +764,13 @@ jobs:
           echo "CXX=g++-${vers}" >> $GITHUB_ENV
         else
           echo "SDKROOT=$(xcrun --sdk macosx --show-sdk-path)" >> $GITHUB_ENV
-          #Use clang-15 and clang++-15 compiler that is installed on runner, instead of one
-          #provided by MacOS (could brew install clang-16/17 to use consistent version
-          #of clang)
-          echo "CC=$(brew --prefix llvm@15)/bin/clang" >> $GITHUB_ENV
-          echo "CXX=$(brew --prefix llvm@15)/bin/clang++" >> $GITHUB_ENV
+          if [[ "$ARCHITECHURE" != "x86_64" ]]; then
+            echo "CC=$(brew --prefix llvm@18)/bin/clang" >> $GITHUB_ENV
+            echo "CXX=$(brew --prefix llvm@18)/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
+          fi
         fi
       env:
         compiler: ${{ matrix.compiler }}