Let clang decide ASan linker flags for the host.

Pass -fsanitize=address instead of manually specifying asan libraries
and other linker flags.

Note that we enable LOCAL_ALLOW_UNDEFINED_SYMBOLS by default for host
builds because ASAN only links symbols in the final executable, so
there will _always_ be undefined symbols in intermediate libraries.

Bug: 18208352
Change-Id: Ief55ab296e94974560eeb10507ec8d90f0025d5c
Add a SANITIZE_HOST flag.

We had discussed the idea of making all host tools default to using
ASAN. Even if we don't make it the default, this makes it easy for the
user to switch all host binaries over.

Change-Id: I64a5c741b1b4e9aefed3a6be8dcd4f386e06b29c
Merge "Let clang decide ASan linker flags for the host."
Merge "Add a SANITIZE_HOST flag."