8264650: Cross-compilation to macos/aarch64

Reviewed-by: burban
Backport-of: 7f9ece2

Author: Vladimir Kempik

make/autoconf/flags.m4

@@ -258,6 +258,14 @@ AC_DEFUN_ONCE([FLAGS_PRE_TOOLCHAIN],
     fi
   fi
 
+  if test "x$OPENJDK_TARGET_OS" = xmacosx; then
+    if test "x$OPENJDK_TARGET_CPU" = xaarch64; then
+      MACHINE_FLAG="$MACHINE_FLAG -arch arm64"
+    elif test "x$OPENJDK_TARGET_CPU" = xx86_64; then
+      MACHINE_FLAG="$MACHINE_FLAG -arch x86_64"
+    fi
+  fi
+
   # FIXME: global flags are not used yet...
   # The "global" flags will *always* be set. Without them, it is not possible to
   # get a working compilation.