Support sanitizing a single device arch

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