set MACOSX_DEPLOYMENT_TARGET for arm64 build

osx_utils.sh

@@ -450,6 +450,7 @@ function macos_arm64_build_wrap {
     export ARCHFLAGS+=" -arch arm64"
     export FCFLAGS+=" -arch arm64"
     export FC=$FC_ARM64
+    export MACOSX_DEPLOYMENT_TARGET="11.0"
     export LDFLAGS+=" -arch arm64 -L$BUILD_PREFIX/lib -Wl,-rpath,$BUILD_PREFIX/lib ${FC_ARM64_LDFLAGS:-}"
     # This would automatically let autoconf know that we are cross compiling for arm64 darwin
     export host_alias="aarch64-apple-darwin20.0.0"