build: Add HAS_SANITIZE_HOST to Soong config variables

SANITIZE_HOST is still used in some .mk files but lacks a corresponding
Soong config variable. This change adds HAS_SANITIZE_HOST to facilitate
the migration to Android.bp.

Bug: 395776750
Test: Add select(soong_config_variable("ANDROID", "SANITIZE_HOST") in
      the Android.bp
Change-Id: I5de4676a2fa1e5f4e901cae189e43902935c1403