xcframeworkbuild.sh: add arm64 simulator target
xcframeworkbuild.sh: add arm64 simulator target

this fixes simulator builds on an M1

Bug: webp:510
Change-Id: Ia2c81d33d9a85b432b17f22305b110ccc337b809

PKRoma/libwebp,webmproject/libwebp,webmproject/libwebp,PKRoma/libwebp,PKRoma/libwebp,webmproject/libwebp,PKRoma/libwebp,webmproject/libwebp,PKRoma/libwebp,webmproject/libwebp,PKRoma/libwebp