Allow specifying one or more architectures to sanitize for. Defaults to
sanitizing all architectures. Allows reducing the cost of sanitization
by only sanitizing half of the platform.
Bug: 29498013
Test: No change to build.ninja files with m -j SANITIZE_TARGET=address
Test: m -j SANITIZE_TARGET=address SANITIZE_TARGET_ARCH=arm
Test: nm -D $OUT/system/bin/app_process64 | grep asan, no asan symbols found
Change-Id: I972cccc2f19443895d47b44bd8104105f93ffb7d