[riscv64][android] skip 2nd abi support for pure 64-bit android For arch riscv, android supports riscv64 only. So, only 64-bit library/module support is needed. So, skip secondary abi support for pure 64-bit android target. co-authors: McKnight22 <tao.wang.2261@gmail.com> Wang Chen <wangchen20@iscas.ac.cn> Bug: angleproject:8165 Change-Id: Ida4def5a6508268d75f107b3c33874dab504230b Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/4563354 Reviewed-by: Cody Northrop <cnorthrop@google.com> Commit-Queue: Cody Northrop <cnorthrop@google.com>