Build: Add option to restrict sanitization by architecture

Add Make variable SANITIZE_ARCH to selectively sanitize binaries.
This uses the "bitness," i.e., 32 or 64, to potentially filter
the sanitization. By default, both are being sanitized.

This can be used to create builds that lower the sanitization
burden by not sanitizing "half" of the platform.

Bug: 29498013
Change-Id: I73e6d479f08a970ba912f4f63967d32f3487125f