Add ld.mcld

As an alternative to ld.bfd in aarch64 where ld.gold doesn't support
To enable it, add "-fuse-ld=mcld -Wl,-maarch64linux" to TARGET_GLOBAL_LDFLAGS
in core/combo/TARGET_linux-arm64.mk (globally), or LOCAL_LDFLAGS (locally).
The "-maarch64linux" switch is needed before aarch64-*4.8 is rebuilt with
upstream patch, see https://android-review.googlesource.com/#/c/91099/

Change-Id: I7dfceb87d2e70a84fd9b4b97400e0dacd210a2ae