try to work around xcode15 linker bug

.github/workflows/apple_m.yml

@@ -98,6 +98,7 @@ jobs:
               make -j$(nproc) DYNAMIC_ARCH=1 USE_OPENMP=${{matrix.openmp}} INTERFACE64=${{matrix.ilp64}} FC="ccache ${{ matrix.fortran }}"
               ;;
             "cmake")
+              export LINKFLAGS="-ld_classic"
               mkdir build && cd build
               cmake -DDYNAMIC_ARCH=1 \
                     -DUSE_OPENMP=${{matrix.openmp}} \