Fix how environment flags are populated

Author: DennisOSRM

.github/workflows/osrm-backend.yml

@@ -215,9 +215,15 @@ jobs:
     runs-on: ${{ matrix.runner || 'ubuntu-24.04' }}
 
     env:
-      BUILD_TYPE: ${{ matrix.type }}
-      CCOMPILER: ${{ matrix.compiler }}
-      CXXCOMPILER: ${{ startsWith(matrix.compiler, 'gcc') && format('g++-{0}', matrix.compiler) || contains(matrix.compiler, 'clang-') && format('clang++{0}', matrix.compiler) || matrix.compiler }}
+      BUILD_TYPE: ${{ matrix.config.type }}
+      CCOMPILER: ${{ matrix.config.compiler || matrix.config.name }}
+      CXXCOMPILER: >-
+        ${{
+          startsWith(matrix.config.name, 'gcc-') && format('g++-{0}', matrix.config.name) ||
+          startsWith(matrix.config.name, 'clang-') && format('clang++-{0}', matrix.config.name) ||
+          matrix.config.name == 'clang' && 'clang++' ||
+          matrix.config.compiler
+        }}
       CXXFLAGS: ${{ matrix.flags }}
       ENABLE_COVERAGE: ${{ matrix.coverage && 'ON' || 'OFF' }}
       ENABLE_SANITIZER: ${{ matrix.sanitizer && 'ON' || 'OFF' }}