Don't use sanitized kati when SANITIZE_HOST=address is set

There used to be CI builds that set SANITIZE_HOST=address, so we
took advantage of that to also run a sanitize version of kati and
ninja.  Those CI builds are no longer active.

Building host fuzzers requires setting SANITIZE_HOST=address, and
sanitized kati is too slow to use for developer builds.  Split out
a separate SANITIZE_BUILD_TOOL_PREBUILTS flag that can be set when
manual testing of sanitized host tool prebuilts is desired.

SANTIIZE_HOST=address will still affect any tools that are built
during the build.

Change-Id: Ifc85d50655aa05e5f0784370086c7203162c8158
Fixes: 278603593
Flag: EXEMPT host-only
Test: manual